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KalexKalina Cycle Power SystemsFor Geothermal Applications

Copyright 2009, 2010, Kalex LLC.

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Kalex LLC's Kalina Cycle for Geothermal Applications

Contents:

Introduction: p.2Section 1; Low Temperature Geothermal p.5Section 2; High Temperature Geothermal p.9Appendix A; System SG-2a p.14Appendix B; Heat Recovery Subsystem p.17Appendix C; DFS (Dual Flash System) p.21Appendix D; System SG-2d p.22Appendix E; Overflood Boiler p.24Table 1; Specific Output Comparison p.27Graph 1; Graph of Specific Output Data p.27Table 2; Thermal Efficiency Comparison p.28Graph 2; Graph of Thermal Efficiency Data p.28Table 3; Second Law Efficiency Comparison p.29Graph 3; Graph of Second Law Efficiency Data p.29Table 4; Relative Output p.30Table 5; Performance Based on Temperature p.30Figure 1; Diagram of SG-2a p.31Figure 2; Diagram of SG-2c p.32Figure 3; Diagram of SG-2d p.33Figure 4; Diagram of SG-4d p.34Figure 8; Diagram of DFS p.35Figure 9; Diagram of Combined Bottoming Cycle p.36Figure 10; Diagram of Combined Parallel Cycle p.37Figure 11; Diagram Heat Recovery Subsystem p.38Graph 5; Heat Recovery Subsystem Graph p.39Figures 13-15; Diagrams of Overflood Boiler p.40

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Kalex LLC's Kalina Cycle for Geothermal Applications

Introduction:

Geothermal energy is currently being used for the production of electric powerthroughout the world, and is increasingly seen as a potential source of "green" power foravoiding emissions of greenhouse gases and atmospheric pollutants. Geothermal power has zeroemissions and uses no fossil fuels. However, the high cost of exploration and drilling makes itcrucial to attain the highest possible degree of cost-effective efficiency.

Kalex offers technology for geothermal applications that gives improved efficiencywithout higher costs. Kalex's geothermal technology allows more power to be generated from agiven geothermal resource, substantially reducing the cost per installed kilowatt of geothermalpower.

Kalex geothermal power systems use only "off-the-shelf" conventional parts, operatingwithin their normal design parameters. No exotic, experimental or costly specialized componentsare required.

Efficiency Advantage:

Kalex LLC's power systems offer substantial improvements in efficiency withoutincreasing the capital costs of the power system. In fact, the overall capital costs of a Kalexsystem are lower than those of a less efficient conventional system. This is possible becauseKalex systems have superior structural efficiency.

The increase in the efficiency of a power system can be achieved only by the reduction ofthermodynamic losses in the thermodynamic cycle used to convert thermal energy intomechanical power. Conceptually, all thermodynamic losses can be divided into three categories;

a) technological thermodynamic losses; losses caused by inefficiency of even state-of-the-art components used to build a system. These reflect the limits of current technologicalability to create these components.

b) economic thermodynamic losses; losses caused by such things as temperaturedifferences in heat exchangers or lower than best available efficiency in the components selectedfor the system. Such losses are deemed "economic" because they are based on suboptimalchoices in equipment made to save money.

c) structural thermodynamic losses; losses caused by the arrangement and innatestructure of the system. Such losses are implicit in the design of the system, and cannot belowered regardless of the quality of components chosen for the construction of the system.

For instance, in a Rankine cycle system with a single component working fluid, boilingoccurs at a constant temperature, whereas most heat sources release heat at variabletemperatures. Therefore, even if the temperature difference at a pinch point were to be zero, therewould still be a substantial thermodynamic loss; this is a typical "structural" loss.

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If an increase in efficiency of a power system is achieved by a reduction of technologicalor economic thermodynamic losses, then this leads, in most cases, to increases in the capital costof the system. A reduction of technological thermodynamic losses requires substantial researchand development costs to develop the improved components. In the case of reductions ofeconomic thermodynamic losses, there is a increased cost due to the selection of the mostexpensive available components, as well as the inevitable cost increases attendant to the use oflarger heat exchangers.

However, if an increase in efficiency is achieved by a reduction of structuralthermodynamic losses, i.e. by introducing a new system with lower innate structuralthermodynamic losses, then it is possible to attain an increase in efficiency without an increase incapital costs.

In fact, a structural increase in efficiency, instead of leading to increased capital costs,actually leads to a reduction of capital costs; less quantity of heat needs to be processed toproduce a given unit of power. This translates to smaller amounts of geothermal resourcerequired per given unit of output.

Moreover, since less heat needs to be processed in the power system, the overall surfaceof the heat exchangers in the power system (which are a major expense) is reduced as well.

Kalex Low Temperature Geothermal Systems:

For low temperature geothermal sources, (below 380 deg. F.,) using Kalex technologyallows profitable utilization of heat sources which are too low-temperature to be cost effectivewith conventional technology. Low temperature geothermal resources which are cost effectivewith conventional technology become far more profitable with Kalex technology. Kalextechnology for low temperature geothermal applications is presented in Section 1 (attached.)

Kalex High Temperature Geothermal Systems:

For high temperature geothermal sources, (from 380 to 500 deg. F., or for any geothermalsource with steam as a substantial part of the resource,) Kalex offers two approaches. Kalexgeothermal systems can be used as a stand-alone power system, delivering improved efficiencywith reduced costs. Alternately, Kalex systems can be used as a bottoming cycle working with aconventional dual flash system, delivering even higher performance at costs comparable or lowerthan the cost of conventional dual flash & bottoming cycle systems. Kalex technology for hightemperature geothermal applications is presented in Section 2 (attached.)

Overflood Boiler for Multi-Component Working Fluid:

Complete vaporization of multi-component working fluid in a conventional boiler isdifficult to attain; though efficient nucleate boiling occurs when the quantity of vapor in thestream of working fluid is small, as vapor accumulates in the boiler the heat transfer coefficientfalls drastically, resulting in large required surface for a heat exchanger.

Kalex offers an innovative, low cost boiler design, applicable to Kalex geothermalapplications and designated an "Overflood Boiler," which is able to efficiently fully vaporizemulti-component working fluids without needing a large heat exchanger surface area.

--A detailed description of this heat recovery subsystem is presented in Appendix E.

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Anti-mineralization Heat Recovery Technology:

Kalex offers a dedicated anti-mineralization heat recovery technology which totallyprevents mineralization in the power system, substantially reducing maintenance costs andallowing highly mineralized heat sources to be safely utilized to a greater extent.

The specific power output of a power system depends on both the initial temperature ofthe geofluid, and on the final outlet temperature of the geofluid. The outlet temperature ofgeofluid is usually limited by the mineralization of the geofluid, or by other considerations, (suchas the further use of the geofluid for heating), which are extrinsic to the structure of the powersystem per se. This limited outlet temperature is hereafter referred to as "LOT." At the same time, any given power system has its own optimal outlet temperature ofgeofluid (hereafter, "OOT.") At this optimal outlet temperature the specific power output reachesits maximum. If the actual outlet temperature is lower or higher than the OOT, the specific poweroutput will be reduced. In cases where the LOT is lower than the OOT, the geofluid should stillbe cooled down only to the OOT; there is no advantage, and in fact there is a disadvantage, incooling it further. Where the LOT is higher than the OOT, there is no conventional recourse butto cool the geofluid down only to the LOT, and accept the reduction in specific power output.

Kalex has developed an approach that allows this to be avoided. By using a heat recoverysusbsystem designed by Kalex, it is possible to cool geofluid to any desired OOT regardless ofthe degree of the mineralization of the geofluid. Moreover, this subsystem totally preventsmineralized geofluid from fouling the internal surfaces of the system's heat exchangers. Thissubstantially reduces maintenance costs and time, and increases the availability of the system.The use of this subsystem also substantially increase the heat transfer coefficient in the heatexchangers where the heat from the geofluid is transferred to the working fluid of the system.Even in cases where mineralization is moderate and the LOT is lower than the OOT, the use ofthis subsystem may therefore be advantageous.

--A detailed description of this heat recovery subsystem is presented in Appendix B.

Non-Geothermal Applications:

Kalex geothermal power systems are also fully applicable to non-geothermal heat sourcesthat provide hear in the same temperature ranges as the geothermal heat sources for which theKalex systems were designed.

Heat sources such as low-temperature solar-thermal and many kinds of industrial wasteheat can be utilized with superior cost effectiveness using Kalex geothermal power systems.

Bottom Line:

Overall, Kalex systems for geothermal applications offer substantial advantages in termsof efficiency and cost effectiveness of geothermal power, allowing for the better utilization ofcurrently viable geothermal resources and for the viable utilization of some geothermal resourceswhich are not cost-effective with conventional power systems.

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SECTION 1

Kalex LLC's Kalina CycleFor Low-Temperature Geothermal Power Systems

The development of power systems utilizing heat from geothermal sources has, in recentyears, been concentrated mostly upon the utilization of liquid dominated geothermal sourceswith moderate or low initial temperatures of geofluid. With such source, the geofluid cannoteffectively be used directly as a working fluid, and instead binary power systems must be used.

The lower the temperatures of such resources, the more geofluid needs to be utilized bythe power system in order to produce a given amount of power. As a result, the cost of geofluidproduction is increased. This also leads to an increase in the costs of the rest of the powersystem, needed to utilize the greater amount of geofluid. The quantity of geofluid required to produce a given amount of power can be reduced byusing a more efficient power system. Therefore, the lower the initial temperature of geofluid, thegreater the importance of the efficiency of the power system designed to utilize these resources.

Legacy Technology:

Till recently, the most commonly used binary power system for geothermal applicationhas been Organic Rankine Cycle systems, or ORC systems. Initially, single pressure ORCs wereused, but more recently dual pressure ORCs, with increased efficiency, have been introduced.

An important disadvantage of an ORC system, besides its relatively low efficiency, isthat the turbine is lubricated with oil. Therefore working fluid vapor at turbine outlet alwayscontains some quantity of oil. As this oil-bearing working fluid enters the system's condenser itcondenses completely and the oil is dissolved in it. As a result, the condensate is a mixture ofworking fluid and oil. This condensate is then pumped by a feed pump and after passing throughthe system's preheater, it enters into the boiler. In the process of boiling, the working fluidevaporates but oil remains in a liquid state. As the operation of the system continues, theconcentration of oil in the boiling liquid inside the boiler increases and the pressure of boiling ofthis mixture at a given temperature, and correspondingly the turbine inlet pressure, decreases.The result is the deterioration of the system and a decrease in the system's power output. Thisphenomena has been observed on all ORC systems with oil lubrication.

A high efficiency alternative to an ORC is a multi-component, variable compositionworking fluid cycle, also known as a Kalina cycle.

The first generation of Kalina cycles applicable to geothermal heat sources consisted oftwo systems, designated KCS-11 and KCS-34. KCS-11 was designed for the higher end of thetemperature range of geothermal resources. KCS-34 was designed for lower temperaturegeothermal resources.

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Kalex Technology:

Kalex LLC has developed four new Kalina cycle power systems based on the concept ofthe reduction of structural losses and designed for the utilization of moderate and lowtemperature (primarily geothermal) heat sources.

These systems, designed to utilize low temperature heat sources, have been designatedSG-2a, SG-2c, SG-2d and SG-4d.

System SG-2a is designed for the utilization of low temperature heat sources, with aninitial temperature of up to 310 °F. (155 °C.)

System SG-2c is a somewhat simplified version of SG-2a.System SG-2d is designed for the utilization of a wide range of heat sources, with initial

temperatures of geofluid up to 400 °F. (205 °C.)It should be noted that, at an initial temperature of geofluid above 310 °F., system SG-

2a's operation degenerates so as to be identical to SG-2d.System SG-4d is designed to operate with a range of initial temperatures from 310 °F to

400 °F or higher. However SG-4d is both more efficient and more complex than system SG-2d.Note that the ranges of operation above are based on an assumed ambient temperature of

59 °F. (15 °C.)If the ambient is higher or lower, the range of operation of each of these systems will

differ accordingly.

--A complete description of system SG-2a (and the related systems, SG-2c, SG-2d and SG-4d) areprovided in Appendix A.

--A flow diagram of system SG-2a is provided in figure 1.--A flow diagram of system SG-2c is provided in figure 2.--A flow diagram of system SG-2d is provided in figure 3.--A flow diagram of system SG-4d is provided in figure 4.

One of the important advantages of the variable composition of the working fluid is thatit allows the system to adapt to changes in ambient temperature. This is a feature that cannot bereplicated in systems with a non-variable working fluid, such as KCS-11 or any Rankine cycle.All of the Kalex SG systems can adjust and react to changes in ambient temperature by changingratio of liquid to vapor when the basic working solution is reconstituted after leaving Separator 1(S1); (for details, see any of the SG series flow diagrams.) This adjustment can be carried outautomatically, without any interruption of normal operations of the system. As a result, theannual power production of a Kalex SG system will be substantially higher than that of a systemwith equal installed capacity that is unable to adjust to variations of ambient temperature.

Efficiency and Output Comparisons:

The advantage of Kalex's SG systems can be seen in a comparison of the SG systems toother binary cycles. There are two criteria of comparison; the thermal efficiency of the systemsand their specific power output. The efficacy of any particular power system depends not only onits thermal efficiency but also on its ability to utilize the thermal energy of the stream ofgeofluid. Therefore, the most accurate means of evaluating the comparative performance of

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geothermal power systems is to compare their specific power output, i.e., the net power outputper unit (by weight) of geofluid flow.

Specific power output takes into account all facets of the actual operational performanceof a power system. For instance, by utilizing and processing more heat from a given heat sourceat a moderate thermal efficiency, a power system with a high specific power output can producemore power from that heat source than another power system which has a higher thermalefficiency but cannot process as much heat from the heat source (and thus has a lower specificpower output.) Thus it is the specific power output, even more than thermal efficiency, thatshows the clearest criteria of effectiveness for geothermal power systems.

The power output of different binary power systems has been calculated assuming anidentical flow rate of geofluid (1,000,000 lb/hour) and subject to the identical ambient conditions(air temperature of 59 °F. and initial cooling water temperature of 51.7 °F.)

Note that the same set of technological constraints (turbine efficiency, pinch pointtemperature differences, etc.,) were assumed for all systems except for the ORC; data for theORC was calculated taking into account the ORC system's gearbox, which results in a reductionof the overall generator efficiency. Because the ORC's working fluid, which is almost alwayshydrocarbon, has a high molecular weight. the ORC turbine operates at a very high RPM andthus requires a gearbox between its turbine and its generator. Systems with water or water-ammonia working fluids do not have this requirement.

--The power outputs of the systems noted above are shown in table 1.--The power outputs of the systems are also presented in the form of a graph in graph 1.--The thermal efficiencies of the systems noted above are shown in table 2.--The thermal efficiencies are also presented in the form of a graph in graph 2.--Thermodynamic ("2nd Law") efficiencies of these systems are shown in table 3.--Thermodynamic ("2nd Law") efficiencies are also presented in a graph in graph 3.

As can be seen from this data, the SG series of systems outperform both the 1stgeneration Kalina cycle systems, and to an even greater degree, the ORC systems.

As can also be seen from the data, system SG-4d provides only a slight improvementover SG-2. Therefore the use of SG-4d is suggested only for relatively large applications wherethis advantage becomes significant.

Kalex Heat Recovery Subsystem & Overflood Boiler:

Kalex's Heat Recovery Subsystem (shown in appendix B) and Overflood Boiler (shown inappendix E) are fully applicable to Kalex low temperature geothermal systems.

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SECTION 2

Kalex LLC's Kalina Cycle for High Temperature Geothermal Applications

Geothermal energy is currently being used for the production of electric powerthroughout the world, and is increasingly seen as a potential source of “green” power foravoiding emissions of greenhouse gases and atmospheric pollutants.

Kalex LLC has developed technology for utilization of high temperature (380 to 500 °F.)geothermal resources. This technology, which relies on the “Kalina Cycle” power cycle, offersthe potential for increased power generation, lower cost, lower maintenance, and reduced well-field degradation.

Legacy Technology; Conventional Geothermal Power Generation:

The earliest use of geothermal resources for power generation involved the use of hightemperature geothermal sources. Such sources, with an initial temperature of between 380 and500 °F, produced geofluid in the form of steam, or more frequently, in the form of a liquid-steammixture. Conventional utilization of such resources involves the use of dual flash power systems,in which steam is used as the working fluid of the power cycle.

--A conceptual flow diagram of a typical dual flash system (DFS) is given in figure 5.--A complete description of the operation of a DFS system is given in appendix C.

Analyzing the operation of a Dual Flash system, the work potential of the steam shouldbe dealt with separately from the work potential of the liquid.

The utilization of the energy potential of the steam in a DFS is substantially efficient butis limited by the wetness of the steam towards the end of expansion process. This wetness mustnot exceed a fixed limit defined by the turbine's design, usually 10%. A further limitation is thepressure of condensation. The lower the pressure in the condenser the greater the output of theturbine. It is, however, difficult to maintain a pressure of less than 1 psia at the exit from thecondenser. Considering the inevitable loss of pressure inside the condenser, the exit pressure inactual application will generally be 3 psia or higher.

This in turn limits the possible pressure at point 100. If the pressure at point 100 is overlyhigh, then at the exit from the second turbine, at the point where wetness reaches 10%, thepressure will be higher than 3 psi. As a result, a substantial portion of the energy potential of thesteam will be lost.

Therefore, if the initial pressure of the geofluid at point 1 is too high, the geofluid needsto pass through a throttle valve (TV1) in order to obtain the desired pressure at point 100.The utilization of the energy potential of liquid in a DFS is extremely inefficient. A substantialportion of the energy potential of the liquid is lost in throttle value TV2. This does produce someadditional quantity of steam, but the exergy losses in this process are high.

As can be seen from the description of the DFS, stream 107 is reinjected at a relativelyelevated temperature and its heat potential is not utilized. Operators of several dual flashgeothermal systems have added an organic Rankine Cycle (ORC) a bottoming binary cycle at alater date, utilizing the lost potential of the liquid to produce additional power. The total heat

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potential of stream 107 depends on the initial quality of the geofluid at point 100. When stream100 contains a substantial quantity of liquid, the weight-flow rate of stream 107 is relatively highand the additional power generated by a bottoming cycle can be substantial. However, when thequality of the geofluid at point 100 is high (mostly steam) the flow rate at point 107 is small andthe additional power that can be generated by a bottoming cycle is likewise small.

Kalex Technology;

It is possible to use a Kalina cycle designed for low temperature geothermal applicationsas such a bottoming cycle. This will increase the power produced by the bottoming binary cycleas compared to using an organic Rankine cycle, but because the overall heat potential of stream107 is relatively small, the increase will not be very large as compared to the overall powerproduced by the dual flash cycle.

--A conceptual flow diagram of this system, including a binary bottoming cycle, is given in figure 6.

Kalex has developed two alternate approaches to utilizing this sort of high temperaturegeothermal resource. These approaches are designated "parallel combined cycle" and "directutilization."

The first of these, the combined parallel cycle, is based on the separate utilization ofsteam and liquid by two different systems operating in parallel.

--A conceptual flow diagram of a combined parallel cycle is given in figure 7.

Vapor, separated in flash tank, S1, (with parameters as at point 101,) is utilized in a dualflash systems (DFS) as described in appendix A.

Liquid from S1 is utilized as a heat source for a Kalex power system, designated SG-2d.This utilization of the energy potential of the liquid is substantially more efficient than in atraditional DFS.

The second approach is the direct utilization of the entire stream of geofluid as a heatsource for system SG-2d.

As both of these approaches utilize system SG-2d, it is described in detail, below.

--A conceptual flow diagram of system SG-2d is presented in figure 3.--A full description of the operation of Kalex system SG-2d is given in appendix D.

Technologically, if the geofluid to be used in SG-2d is a mixture and vapor, it ispreferable to separate the liquid from the vapor, and to utilize these two streams in two separateheat exchangers, working in parallel or consecutively.

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Evaluation of Potential Power Generation:

The performance of the following systems has been computed;--Dual Flash System (DFS)--DFS with Organic Rankine bottoming cycle (DFS/ORC combo)--DFS with a Kalex SG-2a bottoming cycle (DFS/SG-2a combo)--DFS in parallel with SG-2d(DFS+SG-2d parallel)--SG-2dAll computations have been performed for geofluid having an initial temperature of 400

°F. (204.44 °C.) with different qualities of initial geofluid ranging from 0.15 to 1.0. The weightflow rate for all computations is 500,000 lb/hour (62.9989 kg/sec.) The temperature of coolingwater was assumed to be 51.7 °F. (10.78 °C.), corresponding to ISO conditions.

It should be noted that the data presented in Table 1 are preliminary data. Thecomputations do not take into account the additional power consumption of a DFS systemneeded to maintain a vacuum in the condenser. Also, the reduction of turbine efficiency due towetness is not taken into account in the data presented in Table 4.

--This data is given in table 4.

Effects of Different Conditions:

As shown in Table 1, the most efficient system possible is a parallel installation of a DFSand SG-2d.

The use of SG-2a as a bottoming cycle with a DFS is substantially more efficient that theuse of an ORC as a bottoming cycle, but is less efficient that the use of SG-2d in parallel with theDFS.

In general, the incremental increase in output for all systems, including DFS, is quitesmall for very high quality geofluid. At a quality of 0.80 or better, the use of any bottoming orparallel cycle is not likely to be economically justifiable.

The use of SG-2d on its own, with no DFS, has slightly a lower output (from 2.5 to3.05% lower) than the output of a DFS + SG-2d parallel system, but SG-2d used on its own hasthe advantage of much lower costs since it uses only a single turbine, whereas a DFS uses twoturbines and both the parallel DFS + SG-2d and the DFS + bottoming cycles use three turbines.The cost savings from the smaller number of turbines substantially exceeds any extra costs of theextra heat exchangers in the SG-2d system.

The advantage in power output of a parallel system over the direct use of SG-2d ishighest at an initial geofluid temperature of 400 °F operating at ISO conditions.

At these conditions, the DFS portion of a parallel system is capable of expanding steamto the lowest allowable pressure without exceeding 10% wetness at the end of the expansion ineither the first or the second turbine.

If the initial temperature and pressure of the geofluid are higher, the requirement to keepwetness no higher than 10% means that the steam cannot be expanded to the lowest allowablepressure. Therefore, even though the initial temperature and pressure are higher, there would be areduction of power output as compared with the power output at 400 °F. In this case, the steamneeds to be throttled to a lower pressure before entering the turbines. This throttling reduces theoverall thermodynamic efficiency of the process.

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E.G., for an initial temperature of geofluid of 450 °F. with a corresponding pressure of422.47 psia and a quality of 30%, the steam needs to be throttled to a pressure of approximately270 psia.

In this case, the output of the parallel system would be 16,770.34kW, (10,851.28 from theDFS and 5,919.06kW from the SG-2d portion.)

In comparison, the direct use of SG-2d at these same parameters produces 16,484.85kW.Thus the advantage of the parallel system over the direct use of SG-2d is only 1.73%.

In cases where the initial temperature of the geofluid is lower than 400 °F., the operationof a DFS begins to deteriorate. Although the high pressure turbine of the DFS is still capable ofexpanding steam to the lowest allowable pressure without exceeding 10% wetness at the end ofthe expansion, the low pressure turbine of the DFS has a reduced pressure ratio of expansion andthe power generated by the low pressure turbine is reduced proportionally.

At a temperature of 280 °F or lower, all expansion occurs in the high pressure turbine andthe low pressure turbine is rendered totally useless.

At these reduced temperatures, Kalex system SG-2a can be used as a direct powersystem, in the same manner as the "SG-2d direct" approach shown above. At temperatures in therange of approximately 360 °F. or lower, SG-2a will provide superior output than a DFS parallelsystem.

(As noted above, a conceptual flow diagram of system SG-2a is presented in figure 1 and a fulldescription of the operation of Kalex system SG-2a is given in appendix A.)

The difference in the performance can be seen in a table of outputs calculated forgeofluid with a quality of 30% over a range temperatures (from 450 to 260 °F.)

--This data is given in table 5.

It should be noted that as the temperature of the cooling medium (air or water) goes up,the effect is the same as if the temperature of the geofluid were lower.

In particular, in cases where the temperature of cooling air or water is 80 °F or higher theeffect is similar to that shown with a temperature of 280 °F or lower; i.e., all expansion in a DFSoccurs in a single turbine. Therefore, as is the case at low geofluid temperatures, at such highambient temperatures, the second turbine gives so little added output (if any) that it's use is noteconomically viable.

In these cases, such as might occur in tropical conditions, the advantage of a parallelsystem over a direct use of a single SG-2 system is reduced or eliminated, and the direct use ofSG-2 (in these conditions, SG-2a,) gives a higher output as well as a lower cost.

Kalex Heat Recovery Subsystem & Overflood Boiler:

Kalex's Heat Recovery Subsystem (shown in appendix B) and Overflood Boiler (shown inappendix E) are fully applicable to Kalex high temperature geothermal systems.

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Analysis:

The direct use of geothermal fluids in DFS expansion cycles has several drawbacks thatare not apparent from the assessment of net power generation. These drawbacks, which areassociated with the low temperatures and pressures obtained by the geofluid, are reduced oreliminated by using a single SG-2d system.

The first drawback of the DFS system is the very low pressure in the condenser requiredto obtain complete expansion of the vapor through the turbine. SG-2d condenses the geofluid atan elevated pressure, leading to a substantially reduced power requirement for the reinjectionpumps. In some cases, it may be possible to use the well-field production pumps to provideenough pressure to reinject the geofluid with no further pumps, using only the exit pressure ofthe SG-2d system. This would eliminate both the initial cost and the ongoing maintenanceexpense associated with the reinjection pumps.

The second drawback is the need to remove and dispose of incondensable gases.Geofluids usually contain impurities in the form of incondensable gases, typically includingcarbon dioxide, hydrogen sulfide, or sulfur oxides. The removal of these incondensables, whichare often highly corrosive, requires the installation of vacuum pumps or compressors. The powerrequirements for these systems have not been deducted from the net power estimates shown inTable 1. In an SG-2d system, however, complete condensation of geofluid occurs at elevatedpressures; typically requiring no more than a 20 psi pressure drop from the system inlet.Consequently, a simple, and far less costly, separator can remove incondensables. This removaloccurs at a much higher pressure than for the DFS systems, resulting in lower cost and powerrequirements for reinjection equipment, if any is required. If the system pressure provided by theproduction pumps is adequate, there may be no need for separate reinjection equipment for theincondensable gases.

The third drawback of DFS systems is that reinjection of cold geothermal fluid typicallyresults in gradual degradation of the geothermal well field. SG-2d returns the geofluid at a higheraverage temperature than does the DFS system, which will reduce the rate of degradation.The fourth drawback of the DFS system is the need for frequent maintenance to clean the turbineand condenser surfaces. Geofluids almost invariably include dissolved solids. As the fluid iscooled, the saturation point of the water is reached and the excess solids are deposited onequipment surfaces. It is necessary to shut down the power cycle to open and clean theequipment. By using a closed loop cycle of clean ammonia-water mixture, SG-2d removes anypotential for deposition of mineral solids on the turbine or in the condenser. In addition, becausethe exit temperature of the geofluid is much higher in SG-2d than in the condenser of the DFS,solids deposition through the heat exchangers is substantially reduced or completely eliminated,what should result in greater availability of the power plant.

Note that the if Kalex's heat recovery susbsytem (see appendix B) is used as well, itremoves even the limited possibility of mineralization deposition in the heat exchanger apparatusthat might occur with SG-2.

An additional consideration is the system complexity. The dual flash system requireseither two turbines or a turbine with intermediate withdrawal and reintroduction of the steam.

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Dual flash systems with bottoming cycles require a third turbine along with the equipment andmaintenance associated with the auxiliary power cycle. The SG-2d system by itself has only asingle turbine. Moreover, this turbine operates with a lower wetness at the turbine exit*, whichis likely to result in lower maintenance, reduced cost, and higher turbine efficiency.(*The presence of liquid at the turbine exit provides the potential for impact of the liquid on theturbine blades, resulting in potentially higher rates of erosion and increased maintenance costs.Although specialized turbines have been proposed for higher liquid loads, these represent anadditional cost. In addition, the presence of liquid water through a turbine stage is known toreduce the efficiency of the stage, typically by about 1 percentage point for each percentageincrease in the average wetness through the stage.)

Thus, although a dual flash system provides excellent utilization of the heat source atvery high quality levels of geofluid (80% and above), it is not competitive with an SG-2d systemwith lower qualities of geofluid.

At geofluid quality levels lower than 80%, Kalex systems provide significantimprovements over either the DFS system or the DFS with a conventional ORC bottoming cycle.For maximum energy recovery, the best choice is a DFS system for the vapor component of thegeofluid and a parallel SG-2d system for the liquid component. For maximum cost effectiveness,using the SG-2d system by itself imposes a modest penalty in power output (about 3 % comparedto DFS with parallel SG-2d,) but eliminates the need for the entire DFS train, (including twoturbines, a vacuum condenser, high pressure reinjection pumps, and equipment for capturing andreturning incondensable gases.)

SG-2d offers several other advantages. Even at very high qualities of geofluid (from 80 to100% steam), the SG-2d system provides a comparable power output to a DFS system,producing more than 97% of the output of a DFS. (For geofluid qualities below 80%, SG-2dproduces more power than a DFS.) Moreover, the SG-2d system delivers this performance usingonly a single turbine instead of two and without exposing its turbine to the geothermal brine. TheSG-2d system also has the advantages of a higher reinjection temperature for the geothermalbrine and smaller losses from capturing and returning incondensable gases.

In any given real-world application, determining the best system to utilize would requiremore detailed analysis of the cost of the systems for specific well conditions. However in mostcases an SG-2d system will offer both lower costs and better performance than a DFS. In a fewcases, where the quality of the geofluid is very high and maximizing output is worth increasedcosts, a DFS system with an SG-2 bottoming cycle offers somewhat higher performance at ahigher cost. In all cases, Kalex technology offers lower costs, higher performance, or both.

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Appendix A:System SG-2a

System SG-2a is structured as a "cycle within a cycle," or a "built-in cascade."The system's working process is comprised of two interacting cycles, the main cycleand the internal, supporting cycle.

The system is presented in figure 1 and operates as follows;

Fully condensed working fluid of the main cycle (see point 1) is pumped by feedpump P1 and is preheated in counterflow by a returning stream of working fluid in heatexchanger HE2 where it reaches a state of saturated liquid (point 3). Thereafter theworking fluid, having been separated into two substreams, is partially boiled in heatexchangers HE3 and HE4; in heat exchanger HE4 heat is supplied by heat-sourcegeofluid. In HE3 heat is supplied by recuperation from a returning stream that will bedescribed below.

Then the two substreams of working fluid are recombined as one stream (point 8)and then mixed with a stream of recirculating working fluid from the internal cycle. Thismixed stream (point 10) passes through heat exchanger HE5 where it boils, heated bythe geofluid heat source, obtaining parameters as at point 11.

The mixed stream (point 11) is then sent into a separator, S2, where it isseparated into saturated vapor (point 13, also designated as point 16) and saturatedliquid (point 12, also designated as point 15.)

The saturated vapor may then be slightly superheated by the heat-sourcegeofluid in heat exchanger HE6 and is sent into the turbine, T1, where it expands,producing power. (Note that this process may be omitted.)

The liquid from separator S2 (point 15), is throttled (in throttle valve TV1) andthen (point 19) is sent into separator S3 where it is again separated into saturated liquid(point 31) and saturated vapor (point 30.)

The liquid at point 31 is "leaner," i.e. has a lower concentration of the low-boilingcomponent than the liquid exiting separator S2 (at point 12.) This liquid is then againthrottled (in throttle valve TV2) and then mixed with the stream leaving the turbine, T1,(see point 18). This then forms the "returning" stream (point 20.)

The returning stream passes through heat exchanger HE3, where it partiallycondenses, releasing heat used for the boiling of one of the two separated substreamsof the main cycle working fluid (as described above.) Thereafter the returning streamexits from HE3, (point 21) and is then sent into a gravity separator, S1, where it isseparated into saturated vapor (point 22) and saturated liquid (point 23.)

The saturated vapor is then recombined with part of the saturated liquid (point25,) so as to restore it to the same composition as that of the working fluid of the maincycle. This stream (point 26) is then sent into heat exchanger HE2 where it is furthercondensed, releasing heat for the pre-heating of the upcoming stream of main cycleworking fluid (see above) and then exists HE2 in a partially condensed, liquid-vapormixture state (point 27.) Then this stream is sent into a final condenser, HE1, where it isfully condensed in counterflow with a stream of coolant (water or air , points 51-52.)

15

Coolant, with initial parameters as at point 50, is pumped by pump P4, obtainingparameters as at point 51, and enters into HE1 (see above.)

Meanwhile, the main portion of liquid from separator S1 (point 24) is pumped bya circulating pump, P2, to an intermediate pressure (see point 9) which is equal to thepressure in separator S3. Then the stream of vapor from separator S3 (see point 30) ismixed with this liquid, forming a stream of enriched internal cycle working solution (point28). The mixing of the vapor at point 30 and the liquid at point 9 occurs at anintermediate pressure. This pressure is such that, as a result of the mixing, the liquidfully absorbs the vapor. Thus the state of the working fluid at point 28 corresponds to astate of saturated or slightly subcooled liquid.

Thereafter this stream of enriched internal cycle working fluid is pumped (by arecirculating pump P3) to a pressure (point 29) equal to the pressure at point 8 (seeabove) and is then mixed with a stream of main cycle working fluid (point 8, see above)forming a mixed stream (point 10) which is sent into heat exchanger HE5 (see above.)

As noted above, the total process in system SG-2a is comprised of two cycles,the main and the internal cycle. To better understand the process of the system it isuseful to track the process of the working fluid in each of these cycles (which comprisethe overall system.)

The working fluid of the main cycle goes through the following process; theworking fluid fully condenses in HE1, is pumped by pump P1, preheated in HE2,partially vaporized in HE3 and HE4, and then is completely vaporized in HE5, passesthrough separator S2 and superheater HE6, then enters the turbine (T1) where it isexpanded. Then the main cycle working fluid passes through HE3 where it is partiallycondensed, then passes through separator S1, and thereafter, after passing throughHE2, where it is further partially condensed, enters into HE1 where it is fully condensed.

The working fluid of the internal cycle goes through the following process; fullycondensed liquid (point 24) is pumped by P2 to an intermediate pressure, (see point 9)and is then enriched by mixing with vapor from separator S3 (point 30). The liquidabsorbs this vapor, and is then pumped by P3 to an elevated pressure that allows it tobe mixed with the working fluid of the main cycle (at point 10.) Then as part of thismixed stream, the internal cycle working fluid passes through HE5 where it initiallydesorbs and then boils (after the temperature of the mixed stream reaches atemperature equal to the boiling temperature of the internal cycle working fluid,) andthen enters into separator S2. In S2, the internal cycle working fluid is separated intosaturated liquid and saturated vapor. The saturated vapor of the internal cycle workingfluid (which is mixed with vapor of the main cycle working fluid, see point 16) may thenbe superheated in HE6, obtaining parameters as at point 17. Thereafter stream 17 issent into the turbine, T1.

The remaining liquid of the internal cycle working fluid from S2 (points 12 and 15)is then throttled (in TV1) and sent into separator S3 where a stream of very rich vapor(point 30) is separated out. Liquid from S3 is then throttled (in TV2) and mixed with thestream of turbine exhaust (point 18.) The vapor from S3 (point 30) is meanwhile mixedwith subcooled liquid of internal cycle working fluid (point 9) thus forming enrichedworking fluid of the internal cycle (point 28). The enriched stream of internal cycle

16

working fluid (at point 28) is then pumped (by P2, see above.) Thus, the internal cyclerejects its heat to the working fluid of the main cycle, providing heat for boiling in HE3.

As previously noted, SG-2a, can be simplified as follows;The flow rate of internal cycle working fluid can be reduced to such a level that it will befully desorbed and vaporized in HE5 (see above.) In this case the system will have noneed of separators S2 or S3. Such a further simplification is designated as SG-2d (seeappendix D.)

It is important to note that the rate of circulation of the internal cycle working fluidis limited. The heat load of the heat source geo-fluid can be divided into two parts; thehigh temperature part, which occurs in HE6 and HE5, and the low temperature, whichoccurs in HE4. If the rate of circulation is increased then the heat load in HE 5 and HE6is increased. But at the same time, the rejection of heat from the internal cycle in HE3 isincreased as well. As a result the required heat load from the geofluid in HE4 isreduced. Therefore, the rate of circulation of the working fluid in the internal cycle islimited by the fact that the flow rate of the geofluid through HE6 and HE5, is the sameas the flow rate of geofluid through HE4.

As a result of the combination of the two cycles in the SG-2 systems, heatrejection into the ambient is fixed by the heat rejection of the main cycle only. Whereasthe circulation of the working fluid through the turbine is defined by the sum total ofcirculations in both the main and in the internal cycle. The circulation through the turbinein SG-2 is always greater than the flow rate of the working fluid in the main cycle, i.e.the flow rate through the condenser HE1, where the rejection to ambient occurs. It isexactly this phenomenon that is the reason that SG-2 systems have a substantiallyincreased efficiency as compared to any system in which the flow rate of working fluidthough the turbine is the same as the flow rate of working fluid through the finalcondenser.

If, by way of further simplification, the circulation of the working fluid through theinternal cycle is fully eliminated, then the primary advantage of the SG-2 systems isremoved and an SG-2 system converts into the functional equivalent of the 1stgeneration Kalina KCS-11 system. The result of this is a further decrease in theefficiency of the system.

17

Appendix B:Heat Recovery Subsystem

The Kalex Heat Recovery Subsystem is designed to aid in heat recovery fromgeothermal heat sources which are highly mineralized, limiting the amount of heat thatcan be recovered by the direct transfer of heat from the heat source to the powersystem.

Highly mineralized geothermal brine which is cooled in the process of heatrecovery will, at some given temperature, start to release or precipitate solid minerals(mostly silica) which will settle on the surface of heat transfer equipment drasticallyreducing the heat transfer coefficient of the equipment. After some time, thecontaminated heat exchangers will become completely blocked and unworkable.

In some cases, this problem has been addressed by the use of direct contactheat exchangers. In these direct contact heat exchangers a liquid heat transfer fluid(which was immiscible with the heat source liquid) was brought into direct contact withthe liquid heat source. The heat transfer fluid was thus heated as it cooled the heatsource liquid.

Because the heat source liquid and the heat transfer fluid in this arrangementboth have more or less constant specific heat values, the heat recovery in this processis thermodynamically very efficient. Moreover the heat transfer coefficients in suchdirect contact heat exchangers are higher than in conventional heat exchangers.

In this approach, as the heat transfer fluid and the heat source liquid move incounter-flow, the only driving force for this movement is the differing specific gravity ofthese liquids.

For purposes of heat recovery from geothermal brine, oils or liquid hydrocarbonsare usually used as the heat recovery liquid in this approach.

Because the difference in the specific gravity of the heat transfer fluid and theheat source liquid is usually quite small, the velocity with which both liquids move has tobe quite low to avoid flooding of the direct contact heat exchanger.

An alternate approach in the prior art was used by the Barber-Nichols company,where an Organic Rankine Cycle working fluid (usually isobutane or isopentane) wasvaporized in direct contact (in counter-flow) with geothermal brine. However, a singlecomponent working fluid boils at a constant temperature, whereas the heat released bythe geothermal brine is released at variable temperatures. Therefore, this approach,while useful for the vaporization of an ORC working fluid, is not efficient for heatrecovery in cases where the heat recovery fluid is then used to transfer heat to analternate working fluid of a power cycle.

18

To attain efficient heat recovery from liquid heat sources with the use of boilingheat transfer fluid, the boiling of the heat transfer fluid has to occur at variabletemperature which covers the whole range of the temperature change of the heatsource liquid. Moreover, the temperature difference between the heat source liquid andthe boiling heat transfer fluid has to be maintained to be constant of close to constantthroughout the entire process. In other words, the change in enthalpy of the boiling heattransfer fluid must be linear with the change of its temperature.

The Kalex Heat Recovery Subsystem is a direct contact heat exchanger thatuses a multi-component mixture of hydrocarbons as its heat transfer fluid. At least fourdifferent hydrocarbons make up the mixture. Propane, isobutane, pentane, hexane,heptane, octane, nonane and decane can be used as components of the mixture. Inactual operation, the proposed invention, the mixture is chosen so that the boilingprocess of the mixture presents a nearly straight line in coordinates of enthalpy vs.temperature.

The multi-component heat carrying fluid mixture (or "multi-component heatcarrier," hereafter MCHC) is then used in a direct contact heat exchanger. This consistsof a vertical vessel which can be conceptually divided into three parts.

At the top is a space where the heated and vaporized MCHC accumulates. In themiddle is the region where the heat source liquid and the MCHC come into directcontact in counter-flow and the MCHC boils. At the bottom, the cooled heat sourceliquid and the precipitated mineralization are collected. The bottom section of the vesselcan be made of a larger diameter than the middle and top portions of the vessel. Thisreduces the velocity of the brine as it settles into the bottom and allows any MCHC thatmay have been carried down by the brine to float back up.

A diagram of the proposed apparatus is shown in figure 8.

A graph of the process of heat exchange between the heat transfer fluid and theheat source fluid is given in graph 4.

Note that in figure 2, the MCHC is assumed to have a composition consisting of amix of isobutane, pentane, hexane and octane. The pressure of the MCHC is 60psi atthe boiling point and 57psi at the dew point.

The Kalex Heat Recovery Subsystem operates as follows:

Fully heated and fully or partially vaporized MCHC with parameters as at point 1leaves the direct contact heat exchanger and passes through one or more heatexchangers of the power system (or other system that utilizes the heat.) (These arecollectively designated "HE.")

In HE, the MCHC is condensed, releasing heat, and exits HE in the form of a fullycondensed liquid with parameters as at point 2.

19

Stream 2 is then sent into a circulating pump, P, where its pressure is increased,obtaining parameters as at point 3, corresponding to a state of slightly subcooled liquid.

Stream 3 is sent into a direct contact heat exchanger. The stream of MCHCenters the direct contact heat exchanger towards the bottom of the middle section.

Meanwhile, heat source liquid (in general, geothermal brine) with parameters asat point 5 is sent into a pump, P1, where it's pressure is increased to match thepressure of the MCHC in the direct contact heat exchanger, obtaining parameters as atpoint 4, forming a stream of heat source liquid in the state of a subcooled liquid. Thisincrease in pressure is required so that the pressure of the heat source liquid will beequal to the pressure of the MCHC, which, since it has a low boiling point, will be at apressure that is higher than the likely initial pressure of geothermal brine, (or for thatmatter, of any other likely heat source liquid.) A useful side-effect of increasing thepressure of the heat source liquid is that this prevents the presence of water-vapor inthe direct contact heat exchanger, thus avoiding considerable possible complications.

The stream of heat source liquid (stream 4) then enters the direct contact heatexchanger through a spray device at the top of the middle section of the direct contactheat exchanger. The heat source fluid is sprayed down toward the bottom of the directcontact heat exchanger.

The heat source fluid forms multiple droplets which fall and sink through theMCHC that was introduced into the direct contact heat exchanger at point 3.

These droplets of heat source liquid come into direct contact with the MCHC,causing the MCHC to boil. Bubble of MCHC vapor and liquid MCHC move up throughthe direct contact heat exchanger and vaporize as they move upwards, producing drysaturated vapor or wet vapor of MCHC. This vapor accumulates in the top section ofthe direct contact heat exchanger and leaves the direct contact heat exchanger asstream 1 (see above.)

Meanwhile, the droplets of the heat source liquid, in the process of cooling,release dissolved minerals. The cooled heat source liquid and the precipitated mineralssink to the bottom of the direct contact heat exchanger. Here, the heat source liquid isremoved from the direct contact heat exchanger, with parameters as at point 8. Notethat point 8 is beneath point 3, so that the MCHC enters into the direct contact heatexchanger above the point at which the heat source liquid is removed (at point 8.) In thisway, the level of the brine is always above point 8 and thus no MCHC can exit throughthe brine outlet at point 8.

The particles of precipitated minerals collect at the bottom of the direct contactheat exchanger, in the form of a sludge which can be removed periodically through atrap door at the very bottom of the direct contact heat exchanger.

20

Given that the heat transfer coefficients of direct contact heat transfer are veryhigh, the temperature difference between the MCHC and the heat source liquid is verysmall. Due to the linear absorption of heat by the MCHC, these temperature differencescan be maintained almost at a constant level throughout the entire process.

An additional advantage of the Kalex Heat Recovery Subsystem is that the heattransfer (inside HE) from the MCHC to the working fluid of a power system occurs in theprocess of condensation which results in a drastic increase of the overall heat transfercoefficient in HE and thus reduces the required size and cost of the heat exchangerapparatus that makes up HE.

The Kalex Heat Recovery Subsystem provides for efficient heat transfer from anygeothermal heat source liquid with minimum losses of energy potential (exergy.) Itallows geothermal heat source liquid to be cooled to any desired temperature withoutconcern for mineralization or contamination of equipment by the heat source liquid.

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Appendix C:DFS (Dual Flash System)

A DFS (Dual Flash System) is shown in figure 5 and operates as follows:

Geofluid, in the form of a vapor-liquid mixture, with parameters as at point 1, exitsthe production well, PW, passes through a throttle valve, TV1, obtaining parameters asat point 100, and then enters into a high temperature flash tank, S1. Here it is separatedinto saturated steam, with parameters as at point 101, and saturated liquid withparameters as at point 102. The stream of steam, 101, is then sent into a high pressureturbine, T1, where it is expanded to an intermediate pressure, designated "IP,"producing power. It then exits T1 with parameters as at point 104. The steam at point104 is wet, i.e., in a state of liquid-vapor mixture. To prevent mechanical damage to theturbine and turbine blades, it is necessary to limit the wetness of the steam. Althoughexpensive, exotic turbines have been proposed that allow wetness values up to 15%, itis generally necessary to prevent the wetness of the steam from exceeding 10%. If thissteam is allowed to attain a wetness of more than10%, it may result in damage to theturbine.

Meanwhile, liquid with parameters as at point 102 is throttled, in a throttle valve,TV2, to the same pressure as the pressure at point 104, obtaining parameters as atpoint 103. The stream at point 103 is in a state of a liquid-vapor mixture. Because thestreams at both points 103 and 104 are in a state of vapor-liquid mixture with the samepressure, both streams have the same temperature.

Streams 103 and 104 are combined into stream 105, which is then sent into anintermediate pressure flash tank, S2, where it is separated into saturated vapor withparameters as at point 106 and saturated liquid with parameters as at point 107. Stream106 is then sent into a low pressure steam turbine, T2, where it is expanded, producingpower, and obtains parameters as at point 109. The rate of expansion in T2 is limitedsuch that the wetness of the stream at point 109 remains at or below 10% (see above.)Thereafter, stream 109 is sent into a steam condenser, where it is condensed, obtainingparameters as at point 110. Streams 107 and 110 are then pumped by pumps P1 andP2 respectively, to a pressure sufficient for the reinjection of the geofluid into theinjection well (IW,) obtaining parameters as at points 108 and 111 respectively. Streams108 and 111 are then combined into stream 112, which is then sent into the injectionwell, IW.

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Appendix D:System SG-2d

Kalex system SG-2d is shown in figure 3 operates as follows:

Geofluid taken from the wellhead with parameters as at point 40. (This pointcorresponds to point 1 in the diagram of the DFS.) The geofluid is sent into heatexchanger HE6 where it partially condensed, obtaining parameters as at point 41.Thereafter stream 41 is sent into heat exchanger HE5, where it is fully condensed andsubcooled, obtaining parameters as at point 42. Stream 42 is then sent into heatexchanger HE4, where it is further subcooled, obtained parameters as at point 43.Geofluid with parameters as at point 43 is then pumped by a pump, P4, to a requiredpressure, obtaining parameters as at point 112, and is then sent out of the system to thereinjection well.

Fully condensed working fluid, with parameters as at point 1 is pumped to adesired high pressure by pump P1, and obtains parameters as at point 2. Thereafter,the stream with parameters as at point 2 passes through heat exchanger HE2, where itis pre-heated by a returning stream of working fluid (26-27, see below) obtainingparameters as at point 3, corresponding to the boiling point of stream 3. Stream 3 isthen divided into two substreams, having parameters as at points 4 and 5 respectively.Stream 4 then passes through a heat exchanger, HE4, where it is partially vaporized incounterflow by a stream of geofluid (42-43) obtaining parameters as at point 6.Meanwhile stream 5 passes through a heat exchanger, HE3, where it is likewisepartially vaporized, in counterflow with a returning condensing stream of working fluid(20-21) and obtains parameters as at point 7. Thereafter streams 6 and 7 are combinedforming stream 8. Stream 8 is then mixed with a stream of lean liquid having parametersas at point 9 (see below) forming a stream with parameters as at point 10.

Stream 10 then passes through heat exchangers HE5 and HE6 in counterflowwith the stream of geofluid (40-41-42, see above) and obtains parameters as at point17. Stream 17 is then sent into a turbine, T1, where it is expanded, producing work, andobtains parameters as at point 18.

The stream at point 18 is in a state of wet vapor, and the parameters of point 18and point 20 are identical.

The stream with parameters as at point 20 passes through HE3, where it ispartially condensed, providing heat for process 5-7 (see above) and obtainingparameters as at point 21. It then enters into a separator, S1. In separator S1, stream21 is separated into two substreams: a stream of saturated vapor with parameters as atpoint 22 and a stream of saturated liquid with parameters as at point 23.

Stream 23 now divides in two substreams, with parameters as at points 24 & 25.Stream 24 is pumped by pump P2, to a pressure equal to the pressure at point 8,obtaining parameters as at point 9 (see above).

23

Meanwhile, stream 25 is combined with a stream of vapor with parameters as atpoint 22, forming a stream of working fluid with parameters as at point 26. Thecomposition of stream 26 is the same as the composition at point 1. The stream withparameters as at point 26 then passes through HE2, where it is partially condensed,releasing heat for process 2-3 (see above) and obtains parameters as at point 27.Stream 27 is then sent into the final condenser, HE1, where it is fully condensed incounterflow by stream of coolant 50-51, (water or air,) and obtains parameters as atpoint 1 (see above,) completing the cycle.

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Overflood Boiler for Kalex Power Systems

In several processes in Kalex Kalina power systems, it is necessary tocompletely vaporize multi-component variable composition working fluid. However, inpractice, this complete vaporization is difficult to attain. When working fluid, in the formof saturated liquid, is sent into a boiler, the quantity of vapor in the stream of workingfluid is relatively small and the boiling process is characterized as a nucleate boiling.Such a boiling process has a very high film heat transfer coefficient. But as vaporaccumulates in the boiler, a so-called crisis of boiling occurs, and the heat transfercoefficient falls drastically.

When single-component fluids are vaporized, the liquid is recycled within theheat exchanger and nucleate boiling can be sustained throughout the entire process.But, this approach cannot be used directly when it is necessary to vaporize a multi-component fluid, because the vapor produced would have a different composition(having been enriched by the low boiling component).

Therefore, if a multi-component fluid needs to be vaporized fully, or even to asignificant extent, nucleate boiling cannot be maintained for a significant proportion ofthis vaporization. The heat transfer coefficient in such a process is thus very low, andthis results in a very large increase in the required surface of the heat exchanger.

An apparatus for this purpose, designated an "overflood boiler" and designed forboiling and vaporization of multi-component fluids, has been developed by Kalex LLC inorder to achieve the production of vapor of the same composition as the composition ofthe initial multi-component liquid, (in case of complete vaporization,) or else of vaporwhich is in equilibrium with liquid exiting the apparatus, (in case of partial vaporization.)At the same time, the overflood boiler is able to maintain a process of nucleate boiling inthe heat transfer apparatus.

The flow diagram of the overflood boiler is presented in figure 13.

The overflood boiler is comprised from a liquid shell, hereafter referred to as an"LSh," (which is, in essence, a conventional horizontal shell-and-tube heat exchanger,)a vapor shell, hereafter referred to as a "VSh," (which is a horizontal drum or hollowvessel installed above the LSh,) and multiple vertical pipes which connect the shell ofthe LSh with the VSh, hereafter referred to as “connecting pipes” or "CPs."

The entire volume of the LSh shell side, as well as the volume of the CPs and thelower portion of the VSh, is filled with liquid.

The operation of the overflood boiler, where the stream which is to be subjectedto boiling and vaporization is already partially vaporized and must be further but notcompletely vaporized within the apparatus, is described below; the described process isa process of intermediate vaporization, as distinct from initial or final vaporization. In thiscase, the overflood boiler then operates as follows:

25

The heat source stream, which is presumed to be some hot liquid, (e.g.geothermal brine,) having initial parameters as at point 3, enters into the LSh andpasses through its tubes, where it is cooled, releasing heat and leaving the LSh withparameters as at point 4.

The stream to be further vaporized, which is comprised from a stream of vaporand a stream of liquid, enters into the apparatus. The vapor, with parameters as at point1'', enters into the VSh, and the liquid with parameters as at 1', enters into the LSh.

Note that it is also possible to introduce the entire combined flow, vapor andliquid, into the VSh. In this case, the vapor and liquid will separate inside the VSh andthe liquid will flow into the LSh via the CPs.

As a result of heating, the liquid which fills the LSh shell, as well as the CPs andthe lower portion of the VSh, varies in temperature and composition along the length ofthe apparatus; cool and rich in light-component composition at the cold end of theapparatus, and hot and lean in light-component composition at the hot end of theapparatus.

As the liquid boils throughout the apparatus, bubbles of vapor move up andthrough the CPs, entering into the VSh, carrying with them liquid (i.e. creating athermosyphon effect). As a result, a significant quantity of liquid is delivered to the VShwhere it is thoroughly mixed with vapor, bringing the vapor into equilibrium with theliquid. Note that each CP delivers liquid of different temperatures and compositions intothe VSh. Vapor in the VSh is thus brought step-wise into equilibrium with the liquidwhich is in the LSh.

It is important to note that liquid from the VSh can also flow down into the LSh.

As a result, the heat from the heat source fluid is transferred to the boiling liquidin a process of nucleate boiling, and then transferred to the vapor by way of mixing (i.e.direct contact heat and mass transfer).

Vapor produced in the apparatus is then removed from the VSh, havingparameters as at point 2'', where as the remaining, non-vaporized liquid is removedfrom the LSh having parameters as at point 2'.

Due to the intensive mixing of liquid and vapor achieved in the VSh, vapor andliquid with parameters as at points 2'' and 2' are in equilibrium or very close toequilibrium, which is the purpose of the apparatus.

In the case where vaporization in the overflood boiler apparatus is an initialvaporization, (i.e. the stream to be vaporized is comprised of only saturated liquid,) thenvapor is not introduced into the VSh; the apparatus for such an application is shown infigure 14.

26

In the case where vaporization in the overflood boiler apparatus is a finalvaporization, (i.e. all liquid introduced into the apparatus is fully vaporized in it,) then theliquid is not removed from the LSh; the apparatus for such an application is shown infigure 15.

It must be noted that in all three cases, the liquid which is introduced into theapparatus is only a small portion of the total liquid which is contained in the apparatus atany given time.

If needed, such apparatus can be installed consecutively, providing a process ofeffective vaporization of multi-component fluid with a wide range of boilingtemperatures.

Note also that if the whole process of vaporization, from a state of saturatedliquid to a state of saturated vapor, occurs in only one apparatus, the entire streamintroduced into the apparatus is comprised of only saturated liquid, as shown in figure14, and the entire stream removed from the apparatus is comprised only of saturatedvapor as shown in figure 15.

It can be seen, from the previous description, that the boiling process that occursin the liquid shell is pool nucleate boiling.

The film heat transfer coefficient, i.e. the heat transfer coefficient from the boiling side,can be computed from the following equation:

hf = A • q0.7 (where q is heat flux.) (1).

This equation can be transformed into the following format:hf = C • Δt2.3333 (2).

Equation (2) can be used if the boiling liquid is a single component fluid; the value for Aand/or C can be found in most heat transfer data books.

For pure ammonia, equation (2) is given as follows:hf(NH3) = 6.9776 • Δt2.3333 (2a).

For pure water, equation (2) is given as follows:hf(H2O) = 2.02216 • Δt2.3333 (2b).

In order to obtain the film heat transfer coefficient it is first necessary to obtain theinterpolated heat transfer coefficient. This is given as follows:

hi = hf(NH3) • x′ + hf(H2O) • (1-x′) (3).where x′ is the concentration of ammonia in liquid.

Thereafter, the following equation is used to obtain the corrective ratio, R:R = 1 - 1.25(x″-x′)1.12 (4).

Thereafter the actual film heat transfer can be obtained as follows:hf = hi • R (5).

..

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Table 1:Specific Output in Kilowatts per 1,000,000 pounds / hour flow rate:

IT LOT KalexSG-4d

KalexSG-2a

KalexSG-2d

KCS-11 KCS-34 DoublePressure

ORC

SinglePressure

ORC380 ºF 169 ºF 11,935.48 -- 11,799.48 11,380.61 -- 10,220.30 9,460.95370 ºF 166 ºF 11,209.12 -- 11,106.03 10,743.29 -- 9,443.78 8,680.03360 ºF 163 ºF 10,504.33 -- 10,432.30 10,112.04 -- 8,715.56 7,942.29350 ºF 160 ºF 9,812.38 -- 9,772.42 9,488.10 -- 7,970.22 7,246.09340 ºF 157 ºF -- -- 9,121.21 8,872.01 -- 7,302.19 6,585.38330 ºF 154 ºF -- -- 8,464.75 8,251.84 -- 6,700.42 5,996.00320 ºF 151 ºF -- -- 7,810.31 7,635.00 -- 6,107.82 5,415.42310 ºF 148 ºF -- -- 7,162.24 7,023.32 -- 5,547.15 4,856.33300 ºF 145 ºF -- 6,514.65 6,521.37 6,417.08 -- 5,022.59 4,333.26290 ºF 142 ºF -- 5,974.15 5,889.27 5,799.73 -- 4,506.75 3,844.53280 ºF 139 ºF -- 5,451.74 5,267.74 4,858.54 4,696.58 4,030.00 3,387.56270 ºF 136 ºF -- 4,949.56 4,648.09 3,908.60 4,267.92 -- 2,963.94260 ºF 133 ºF -- 4,448.29 4,065.26 2,965.81 3,838.32 -- 2,570.74250 ºF 130 ºF -- 3,962.63 3,552.31 -- 3,429.44 -- --

In the table above: IT is Inlet Temperature.LOT is Limited Outlet Temperature.KCS-11 and KCS-34 are examples of the 1st generation of Kalina cycle systems.ORC is Organic Rankine Cycle.

Graph 1:

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Table 2:Thermal Efficiency Comparison Table:

IT LOT KalexSG-4d

KalexSG-2a

KalexSG-2d

KCS-11 KCS-34 DoublePressure

ORC

SinglePressure

ORC380 ºF 169 ºF 19.07 -- 18.91 18.15 -- 16.06 14.87370 ºF 166 ºF 18.53 -- 18.59 17.72 -- 15.60 14.34360 ºF 163 ºF 17.98 -- 18.19 17.27 -- 15.17 13.83350 ºF 160 ºF 17.42 -- 17.78 16.81 -- 14.66 13.33340 ºF 157 ºF -- -- 17.24 16.32 -- 14.23 12.84330 ºF 154 ºF -- -- 16.56 15.78 -- 13.56 12.13320 ºF 151 ºF -- -- 15.93 15.20 -- 12.84 11.39310 ºF 148 ºF -- -- 15.16 14.59 -- 12.14 10.91300 ºF 145 ºF -- 15.02 14.34 13.93 -- 11.45 10.44290 ºF 142 ºF -- 14.26 13.48 13.19 -- 11.03 9.98280 ºF 139 ºF -- 13.59 12.66 11.60 12.16 10.25 9.54270 ºF 136 ºF -- 12.81 11.73 9.82 11.97 -- 9.11260 ºF 133 ºF -- 11.79 11.03 7.86 11.74 -- 8.70250 ºF 130 ºF -- 11.11 10.40 -- 11.54 -- --

In the table above: IT is Inlet Temperature.LOT is Limited Outlet Temperature.KCS-11 and KCS-34 are examples of the 1st generation of Kalina cycle systems.ORC is Organic Rankine Cycle.

Graph 2:

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Table 3:Second Law Efficiency Comparison Table:

IT LOT KalexSG-4d

KalexSG-2a

KalexSG-2d

KCS-11 KCS-34 DoublePressure

ORC

SinglePressure

ORC380 ºF 169 ºF 63.82 -- 63.21 60.78 -- 53.64 49.65370 ºF 166 ºF 63.27 -- 63.20 60.57 -- 52.91 48.63360 ºF 163 ºF 62.72 -- 63.02 60.30 -- 52.27 47.63350 ºF 160 ºF 62.11 -- 62.82 59.97 -- 51.33 46.66340 ºF 157 ºF -- -- 62.34 59.58 -- 50.67 45.69330 ºF 154 ºF -- -- 61.42 59.02 -- 49.49 44.69320 ºF 151 ºF -- -- 60.56 58.31 -- 48.14 42.68310 ºF 148 ºF -- -- 59.27 57.44 -- 46.77 41.65300 ºF 145 ºF -- 59.48 57.76 56.38 -- 45.42 40.65290 ºF 142 ºF -- 58.35 56.01 54.92 -- 44.67 39.67280 ºF 139 ºF -- 57.43 54,21 49.78 50.72 42.94 38.71270 ºF 136 ºF -- 56.15 51.73 45.50 51.08 -- 37.79260 ºF 133 ºF -- 54.01 50.12 36.01 51.31 -- 36.91250 ºF 130 ºF -- 52.76 48.61 -- 51.68 -- --

In the table above: IT is Inlet Temperature.LOT is Limited Outlet Temperature.KCS-11 and KCS-34 are examples of the 1st generation of Kalina cycle systems.ORC is Organic Rankine Cycle.

Graph 3:

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Table 4:Relative Output of Geothermal Systems:

DFS DFS with ORCbottoming cycle

DFS + SG-2aCombined

DFS + SG-2dParallel

SG-2dDirect

Qualityof

Geofluid NetOutput(kW)

NetOutput(kW)

%OutputIncrease

NetOutput(kW)

%OutputIncrease

NetOutput(kW)

%OutputIncrease

NetOutput(kW)

%OutputIncrease

0.15 7910.27 8882.15 12.29 9502.47 20.13 10894.64 37.73 10592.15 33.900.30 12843.64 13667.36 6.41 14193.10 10.51 15301.35 19.14 14849.05 15.610.45 17777.00 18452.55 3.80 18883.73 6.23 19708.06 10.86 19150.79 7.730.60 22710.37 23237.75 2.23 23574.36 3.80 24114.78 6.18 23470.16 3.350.80 29288.19 29618.02 1.13 29828.54 1.84 29990.40 2.40 29238.63 -0.171.00 35866.01 35998.28 0.37 36082.71 0.60 35866.01 0.00 35015.09 -2.43

--Quality of Geofluid is given as a proportion of steam to liquid; 1.00 represents pure steam.--"DFS" is a Dual Flash System--"ORC" is an Organic Rankine Cycle--"% Output Increase" shows change in output compared to a DFS with the same geofluid quality.

Initial temperature of geofluid is 400 °F. (204.44 °C.)Weight flow rate is 500,000 lb/hour (62.9989 kg/sec.)Temperature of cooling water is 51.7 °F. (10.78 °C.), corresponding to ISO conditions.

Table 5:Performance Difference Based on Temperature

Initial Temperature DFS;Output in kW

ParallelDFS + SG-2d;Output in kW

SG-2a direct;Output in kW

Difference between DFS + SG-2aParallel and SG-2a Direct;

450 °F 10851.28 16770.34 16484.85 -1.73%400 °F 10759.28 15301.35 14849.05 -3.05%380 °F 10220.37 14350.19 14136.20 -1.49%360 °F 9634.43 13285.74 13391.31 +0.80%340 °F 9001.17 12193.59 12338.97 +1.19%320 °F 8320.09 11053.70 11184.77 +1.19%300 °F 7590.01 9872.49 10025.20 +1.55%280 °F 6809.25 8717.36 8958.17 +2.76%260 °F 5978.68 7535.87 7928.36 +5.21%

--"DFS" is a Dual Flash System

Geofluid quality is .30.Weight flow rate is 500,000 lb/hour (62.9989 kg/sec.)Temperature of cooling water is 51.7 °F. (10.78 °C.), corresponding to ISO conditions.

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Figure 1:

System SG-2a

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Figure 2:

System SG-2c

33

Figure 3:

System SG-2d

34

Figure 4:

System SG-4d

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Figure 5:

DFS(Dual Flash System)

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Figure 6:

Combined Bottoming Cycle

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Figure 7:

Combined Parallel Cycle

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Figure 8:

Heat Recovery Subsystem

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Graph 5:

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Figures 13, 14 & 15:

Overflood Boiler

For further information, please see Kalex LLC's website, at www.kalexsystems.comTechnical and business inquiries may be sent to information@kalexsystems.com