at SciVerse ScienceDirect

Applied Thermal Engineering 59 (2013) 174e181

Contents lists available

Applied Thermal Engineering

journal homepage: www.elsevier .com/locate/apthermeng

Small scale biomass CHP plant: An assessment for an animal feedindustry

Marcos Luiz de Macedo Rodrigues 1, Felipe Raúl Ponce Arrieta 2, José Ricardo Sodré*

Pontifical Catholic University of Minas Gerais, Department of Mechanical Engineering, Av. Dom José Gaspar, 500, 30535-901 Belo Horizonte, MG, Brazil

h i g h l i g h t s

� Under considered economic scenario CHP plant using wood chips as fuel is not feasible.� Feasibility of CHP plant implementation is achieved using charcoal as fuel.� Best results achieved for 90% boiler efficiency and commercialization of carbon credits.� CHP plant is mostly influenced by electric power price, interest rate and capital investment.� Minimum costs achieved with no electric power selling and maximum turbine steam extraction.

a r t i c l e i n f o

Article history:Received 15 February 2013Accepted 18 May 2013Available online 28 May 2013

Keywords:BiomassCombined heat and powerEnergyExergoeconomic assessmentRankine cycle

* Corresponding author. Tel.: þ55 31 3319 4911; faE-mail addresses: mlmrod@uol.com.br (M.L.M

pucminas.br (F.R.P. Arrieta), ricardo@pucminas.br (J.R1 Tel.: þ55 31 9819 8395; fax: þ55 31 3319 4910.2 Tel.: þ55 31 9614 5380; fax: þ55 31 3319 4910.

1359-4311/$ e see front matter � 2013 Elsevier Ltd.http://dx.doi.org/10.1016/j.applthermaleng.2013.05.03

a b s t r a c t

This paper describes a technical, economic and exergoeconomic assessment to verify the feasibility of acombined heat and power (CHP) plant implementation in an animal feed industry to attend its electricpower demands. A small-scale Rankine cycle was defined for the CHP plant. Plant operation wassimulated at steady state condition, taking into account heat and electric power demands under twoconsiderations: electric power selling to the grid and burning wood chips or charcoal as fuel. In order toget the feasibility assessment, a cash flow was elaborated. The thermoeconomic structural theory wasapplied for the exergoeconomic assessment. The results show that the feasibility of the CHP plantimplementation was achieved by using charcoal as fuel. The consideration of electric power selling to thegrid was shown to be the most interesting.

� 2013 Elsevier Ltd. All rights reserved.

1. Introduction

Many small and medium size industries could benefit from theuse of combined heat and power (CHP) to increase their competi-tiveness. Besides, biomass from various sources such as agriculturewaste, furniture industry waste, reforestation residues, forestsplanted in expansion, etc., can be further exploited by small-scalefacilities [1e3]. Different technologies have been studied forsmall-scale power generation from biomass, using experimental,analytical and simulation approaches. Al-Kassir et al. [4] studiedthe gasification process of different types of cork residues gener-ated by industries in Spain. A preliminary study of a pilot installa-tion of gasification of 50 kWe using these residues was built based

x: þ55 31 3319 4910.. Rodrigues), felipe.ponce@. Sodré).

All rights reserved.1

on laboratory experiments. A 220 kW thermal power plant wasdesigned, considering the energetic characteristics of the residuesfor 50 kg/h of raw material and thermal efficiency of 22.5%.

Vera et al. [5] simulated a small-scale combined heat and power(CHP) plant fueled by olive industry wastes incorporating adowndraft gasifier, gas cleaning and cooling subsystem, and amicroturbine. The product gas obtained has a low heating value of4.8e5.0MJ/Nm3 and the CHP system provides 30 kWe and 60 kWh.High overall CHP efficiencies of around 50% are achievable withsuch systems. Preißinger et al. [6] studied a biomass fired double-stage Organic Rankine Cycle (ORC) for micro-cogeneration. Focuswas laid on optimizing thermal efficiency in summer mode byappropriate working fluid and pressure level selection. Appropriateworking fluid combinations within a double-stage ORC reachedtotal efficiencies of up to 35%.

Loeser and Redfern [7] simulated a system that consists of asmall-scale downdraft gasifier and an anaerobic digester unit, bothcoupled to a gas storage system and a microturbine. This combinedfeedstock design is suitable to provide electric power down to alevel of around 50 kWe, which suits a remote village or a large farm.

0 10 20 30 40 50 60 70 80 90 100YEAR TIME (%)

0

200

400

600

800

1000

POWERDEMAND( kWe)

0

2000

4000

6000

8000

10000

12000

14000

HEAT

DEMAND(k Wt)

POWERHEAT

Fig. 2. Electric power and heat and demand throughout the year.

M.L.M. Rodrigues et al. / Applied Thermal Engineering 59 (2013) 174e181 175

The results showed that the system is a feasible and economic so-lution for remote power supply. Schmidt et al. [8] assessed CHPpotentials using a simulation model that optimizes locations ofbioenergy plants. Investment costs of district heating infrastructurewere modeled as a function of heat demand densities, which candiffer substantially. Heat utilization decreases when CHP produc-tion increases due to limited heat demand that is suitable for dis-trict heating. Production potentials are mostly sensitive to biomasscosts and power prices.

The objective of this work is to perform a technical-economicstudy to analyze the feasibility to implement a CHP plant of elec-tric power cogeneration from biomass in a small-scale animal feedindustry which produces flour from bovine bones (used to manu-facture livestock food) and animal fat (used to manufacture bio-diesel). Fig. 1 shows the energy supply system in continuousproduction lines. The industry has a steam generation system thatburns biomass to assure the heat demand process and it is con-nected to the electric grid, using electric power from the localconcessionaire. During peak hours of consumption a diesel gener-ator is turned on to reduce the costs of electric power. The upgradeof the existing energy supply to the system with a CHP plant isplanned with non-continuous production lines. A Rankine cycle isadded to produce heat (saturated steam) and electric power to theindustrial process using an existing boiler. The surplus or deficit ofelectric power depends on heat and electric power demands of theindustrial process and biomass availability.

Fig. 2 presents the industry annual heat and electric powerdemand, with the following characteristics [9]: at a high value ofheat demand there is a proportional high value of electric powerdemand and vice versa; there are only three typical levels of energyconsumption (high, intermediate and low), and; at steady stateoperation any level of energy demand can be considered constant.The average heat and electric power demands at all energy con-sumption levels are hereby presented. In order to assure the pro-cess heat demand, the current heat generation system consists of aboiler that produces saturated steam for the industrial process from

Fig. 1. Existing energy supply syste

burning of wood chips and charcoal. The boiler has a combustionair preheater and a furnace with a high volume of post-combustionchamber to ensure high combustion efficiency, and allows for thepossibility to install a superheater. The boiler can burnwood chip orcharcoal without any modification in the feeding system. Table 1presents the current boiler operation data, the current annualconsumption, current fuel price and low heating value (LHV), andthe electric power current price and annual consumption.

2. Analytical approach

Full time boiler operation at the nominal steam flow rate tomaximize the surplus of electric power selling to the grid wasinitially considered in the analysis of the implementation of a CHPplant to the industry. Then, the hypothesis of no electric powerselling was also considered, generating the minimum amount ofelectric power necessary to supply the demand. New parameters of

m upgraded with a CHP plant.

Table 1Operational data of energy supply system to the facility.

Parameter Value

Boiler Pressure (kPa) 950Temperature (�C) 177.7Maximum flow (kg/s) 5.55Efficiency (%) 84Temperature of feed water (�C) 80

Wood chip Consumption (ton/year) 34,882Low heating value (kJ/kg) 7745Price, including taxes (US$/ton) 72.00

Charcoal Consumption (ton/year) 12,904Low heating value (kJ/kg) 20,934Price, including taxes (US$/ton) 70.00

Electricpower

Purchase/selling price, includingtaxes (US$/MW h)

112.50

Consumption (kW h/year) 5,242,860

M.L.M. Rodrigues et al. / Applied Thermal Engineering 59 (2013) 174e181176

steam generated in the boiler (2.62 MPa, 300 �C) were consideredfor both alternatives during calculation of the thermal cyclebecause it was previously operated under the nominal parameters.The feasibility assessment was carried out for both types ofbiomass, wood chips and charcoal. The three-criterion feasibilityassessment of the CHP plant implementation included:

- Steam generation in the boiler with current efficiency of 84%,considering only the additional cost with biomass consump-tion due to the new operating condition (base mode);

- Boiler efficiency increased to 90%, considering only the addi-tional cost with biomass consumption due to the new oper-ating condition;

- The same condition as above, with addition of the income fromcommercialization of carbon credits.

Fig. 3. Schematics of oper

Thus, a total of 12 technical and economic assessment modeswere analyzed for the small-scale biomass CHP plant imple-mentation (Fig. 3). Four thermodynamic modes were derived fromthe assumptions of selling or no selling of electric power to the gridand from the use of wood chips or charcoal as boiler fuel. Threemodes had financial aspects, analyzing possible improvementsfrom increased steamparameters and boiler efficiency and from theuse of financial incentives, such as possible commercialization ofcarbon credits.

The peculiarity of the heat demand (see Fig. 2) set the use of acondensing turbine with extraction at the controlled pressure of950 kPa, defining the configuration of the thermal cycle of the CHPplant shown by Fig. 4. At low heat level demand the extractionsteam flow is minimum and the electric power production ismaximum, thus requiring the maximum steam condensation. Theunavailability of water at the industry site location forced the use ofan air cooler condenser. The airflow calculation for condensercooling was carried out considering data from industrial ventilationsystems obtained from Ref. [10].

For cooling purposes, the steam turbine requires a minimum of20% of the nominal steam flow at the outlet of the low pressuresection. In order to assure that the steam extracted from the turbinewould reach the saturation state when it arrives to the process, theCHP thermal cycle incorporates a desuperheater, which reduces thesteam temperature down to 3e5 �C above the saturation temper-ature to compensate heat losses in the pipes. The steam transfersheat to the process indirectly, returning to the CHP plant condensedand demineralized through the deaerator tank, which has thefunction of removing water dissolved oxygen and carbon dioxide.The thermal cycle of the CHP plant has a high pressure regenerativewater heater after the feed water pump, aiming at increasing watertemperature at the boiler inlet. Fuel consumption in thermal cycleswith similar configuration has been reduced [11], allowing for

ation modes studied.

Fig. 4. Schematics of the Rankine cycle for the CHP plant.

M.L.M. Rodrigues et al. / Applied Thermal Engineering 59 (2013) 174e181 177

increased boiler efficiency by 6%. Condensate at the preheateroutlet is drained to a steam trap to the deaerator tank.

3. Methodology

Aiming at maximized use of fuel energy, the CHP plant opera-tion was assumed to follow the heat demand curve. Therefore, inthe case of electric power selling, the CHP plant must assure theheat demand and produce as much electric power as possible.Moreover, in the case of no electric power selling the CHP plantmust guarantee the heat demand and produce electric power withthe minimum deficit regarding the process power demand [11].

Table 2 presents a summary of steam turbine data obtained fromtwo manufacturers, A and B, according to the conditions heredefined. The steam turbines from both manufacturers are able tooperate close to the heat demand curve, but turbine A generatesmore electric power and has a higher price than turbine B. Thus,turbine A was selected to be installed in the CHP plant for

Table 2Steam turbine technical and operational data supplied from manufacturers.

Manufacturer A B

Operation modea 1b 2 3 4 5 6b

Inlet steamPressure (kPa) 2620 2620 2620 2620 2620 2620Temperature (�C) 300 300 300 300 300 300Mass flow (kg/s) 5.55 5.55 5.55 5.55 3.33 1.11Extraction steamPressure (kPa) 950 950 950 950 950 950Temperature (�C) 205 205 205 215 215 215Mass flow (kg/s) 4.44 2.22 0.14 4.44 2.22 0.14Pressure (kPa) 20 20 20 105 105 105Outlet steamPressure (kPa) 20 20 20 105 105 105Temperature (�C) Liquidevapor mixture Liquidevapor mixtureMass flow (kg/s) 1.11 3.33 5.41 1.11 1.11 0.97Generation and priceElectric power (kW) 1135 2190 3270 940 550 200Price (US$) 1,751,900.00 1,250,000.00

a Gearbox efficiency 98%; generator efficiency 95%.b Minimum steam flow in the turbine condensate section.

assessment under the consideration of electric power selling athigh (1), intermediate (2) and low (3) level of energy demand, andturbine B was selected for the consideration of no electric powerselling under operation at similar levels (4, 5 and 6). At all operatingconditions the power at the generator terminals is given by theturbine output powerminus the energy losses in the gearbox and inthe generator.

The estimated capital investment for the economic and sensi-bility analysis did not consider the value related to the boiler,because it already exists in the plant (Table 3). Installation of asteam superheater was considered in “other equipment”. The cycleavailability factor was assumed to be 95% in 8640 h/year. For noelectric power selling, the cost of interconnection between theelectrical substation and the grid is not considered. The cash flowfor electric power selling or not, considering the two types ofbiomass, the current price of electric power and the interest ratewas prepared for all modes to obtain the Net Present Value (NPV),Internal Rate of Return (IRR) and Pay Back (PB). The values adoptedto compute the cash flows are presented in Table 4, from which asensibility analysis was carried out varying the parameters in therange shown. The range of variation for each parameter was chosento attain the best evaluation of the system feasibility. New resultswere obtained considering the same values and income with 90%boiler efficiency with or without carbon credits selling.

Table 3Estimated capital investment for CHP implementation.

Item Investment cost, includingtaxes (US$)

Electricpower selling

No electricpower selling

Electromechanicalequipment

Boiler (45%) 0.00 0.00Steam turbine (35%) 1,751,900.00 1,250,000.00Pipes and others (10%) 175,190.00 125,000.00Electric substation (5%) 87,595.00 0.00Other equipment (5%) 87,595.00 62,500.00Subtotal 2,102,280.00 1,437,500.00Installation (12%) 252,273.60 172,500.00

Construction Execution (15%) 313,449.95 214,331.25Total 2,668,003.55 1,824,331.25

Table 4Data for economic and sensibility analysis.

Parameter Base value Variation range forsensibility analysis

Wood chip price (US$/ton) 72.00 �10% to �50%Charcoal price (US$/ton) 70.00 �10% to �50%Purchase/selling price of

electric power (US$/MW h)112.50 þ10% to þ50%

Interest rate (%) 9.00 �10% to �50%Carbon credits (US$/ton

of equivalent CO2)14.90 [12] þ10% to þ50%

Capital investment (US$) Per Table 2 �10% to �50%

M.L.M. Rodrigues et al. / Applied Thermal Engineering 59 (2013) 174e181178

To perform an exergetic cost analysis, it is useful to define aproductive or causal structure, the counterpart to the physicalstructure used to calculate the system energy and the exergy flows[13]. The productive structure shown by Fig. 5 is a schematic rep-resentation of the plant based on the Fuel-Product concept. Forcalculation of the unit exergetic cost, a model based on the Struc-tural Theory of Thermoeconomic analysis was developed [14]. Thethermoeconomic model is a mathematical representation of theproductive structure of a system [15]. For the CHP plant thefollowing equations define the fuel (F), product (P), irreversibility(I), exergetic efficiency rate (h), unit exergetic consumption (k) andefficiency defect (d):

F ¼ Bbiomass (1)

P ¼ _Wuse þ BQ (2)

I ¼ F � P (3)

h ¼ P=F (4)

Fig. 5. Rankine cycle pr

k ¼ F=P ¼ 1=h (5)

d ¼ 1� h (6)

where Bbiomass is the biomass exergy rate (kW), BQ is the heatexergy rate (kW), and _Wuse is the useful power plant power (kW).

The flows of the productive structure shown that interact withthe external interfaces are: biomass consumed as fuel (flow 1); airfor biomass combustion in the boiler (flow 2); electric power pro-duced for the process (flow 10); electric power consumed from thegrid (flow 12); Condensate water returned from the process (flow43); and heat produced for the process (flow 54) (Fig. 5). Mass andenergy balances obtained through a thermodynamic simulationmodel built using the Energy Equation Solver (EES) software wereused as input data for the economic analysis of the CHP plantimplementation, and to perform the feasibility study and theexergoeconomic assessment.

4. Results and discussion

The NPV results of cash flows performed by the economicanalysis of wood chip were US$ �3.18 million for electric powerselling and US$ �0.49 million for no electric power selling. Theseresults lead to the conclusion that implementation of the CHP plantusing this fuel is not feasible. On the other hand, Figs. 6 and 7 showthe feasibility of CHP plant implementation using charcoal as fuel,with the best results being achieved for modes 6 and 12, whichfeature 90% boiler efficiency and carbon credits commercialization,respectively.

The sensibility economic analysis, based on the variation of NPV,presents the following high to low order of influence on the prof-itability of the CHP plant implementation by using charcoal as fuel,for electric power selling: electric power rate, interest rate, fuelprice, cost of investment and carbon credits (Fig. 8). For no electric

oductive structure.

Fig. 6. NPV variation for charcoal as fuel with electric power selling.Fig. 8. NPV sensibility analysis for charcoal as fuel with electric power selling.

M.L.M. Rodrigues et al. / Applied Thermal Engineering 59 (2013) 174e181 179

power selling the order of influence is: electric power rate, interestrate, investment cost, carbon credits and fuel price (Fig. 9). Anotheraspect that has a major impact on the feasibility of the proposedCHP system is the rate of electric power selling. For charcoal with atariff of electric power of US$ 168.8/MW h (50% above theconsidered), with electric power selling, the NPV is US$ 9.44million(Fig. 8), IRR is 50.25% and PB is 3.3 years. With no electric powerselling the NPV is US$ 3.03 million (Fig. 9), IRR is 29.40% and PB is5.2 years.

The price of electric power can vary due to several factors suchas contracts, market conditions, power supply availability, etc.,which may not rely on the consumer only. On the other hand,charcoal price can be reduced with industry priorities such asfreight cost, long-term contracts, own reforestation, and develop-ment of local biomass cultures. With low charcoal price it is inter-esting to sell more electric power because the PB is attractivelylower (Figs. 6 and 7). Carbon credits have a relatively low impact onNPV because the industry already uses charcoal as fuel and no fossilfuel was replaced (Figs. 8 and 9).

Table 5 presents a summary of the results of the exergetic costanalysis for the CHP plant for the operation modes shown in Fig. 3.Modes 1e3 refers to wood chip with electricity selling, modes 3e6

Fig. 7. NPV variation for charcoal as fuel with no electric power selling.

refers to charcoal with electricity selling, modes 7e9 refers towoodchip without electricity selling, and modes 10e12 refers to charcoalwithout electricity selling. In the CHP plant the main sources ofirreversibility are the boiler, caused by combustion and heattransfer, and the condenser, caused by heat transfer. The more fuelis burned and more steam flows into the condenser, more exergy isdestroyed in both equipment. Considering the hypothesis of elec-tric power selling (operation modes 1e6), the smallest irrevers-ibility is found in operation mode 4, with charcoal as fuel and themaximum mass flow extraction from the turbine. In this case, aminimum amount of steam flows to the condenser, because theprocess is operating at maximum heat demand. With no electricpower selling (operation modes 7e12), the smallest irreversibilityis found in operation mode 12, with charcoal as fuel and the min-imum mass flow extraction from the turbine. In this case there islow fuel consumption in the CHP plant and low steam production inthe boiler.

The lowest costs of electric power and heat at the differentoperation modes are observed when charcoal is used as fuel(modes 3e6 and 10e12 in Table 5), due to its low price (US$ 3.35/GJ) compared with wood chip price (US$ 9.30/GJ) (modes 1e3 and7e9 in Table 5). The lowest values of electric power and heat areUS$ 119/MW h and US$ 17.5/MW h, respectively, obtained in

Fig. 9. NPV sensibility analysis for charcoal as fuel with no electric power selling.

Table 5Results of exergetic cost analysis for wood chip, with electric power selling (modes 1e3) or no electric power selling (modes and 7e9), and charcoal, with electric power selling(modes 4e6) or no electric power selling (modes 10e12).

Operation mode F P I h k d Electric power cost Heat cost

kW kW kW e e e US$/MW h US$/MW h

1 18,531 4392 14,139 0.24 4.22 0.76 1193.5 283.52 18,465 3650 14,815 0.20 5.06 0.80 930 840.53 18,403 3021 15,832 0.16 6.09 0.84 2213 42,040.54 15,775 4392 11,384 0.28 3.59 0.72 411.5 94.55 15,709 3650 12,059 0.23 4.30 0.77 317.5 2776 15,648 3021 12,627 0.19 5.18 0.81 352 67497 18,531 4122 14,408 0.22 4.50 0.78 306.5 48.58 11,109 2148 8961 0.19 5.17 0.81 623.5 1029 3685 322 3364 0.09 11.46 0.91 2552 1833.510 15,775 4122 11,653 0.26 3.83 0.74 119 17.511 9453 2148 7305 0.23 4.40 0.77 224 3512 3133 322 2811 0.10 9.74 0.90 895.5 624.5

M.L.M. Rodrigues et al. / Applied Thermal Engineering 59 (2013) 174e181180

operation mode 10, with no electric power selling and usingcharcoal as fuel. Those values are due to the low cost of investment,if compared to the modes with electric power selling, and the lessamount of steam that flows to the condenser. The highest costs arefound for the modes with minimum mass flow extraction in the

Fig. 10. Total cost of CHP plant for the operation modes.

Fig. 11. Exergetic efficiency of CHP plant for the operation modes.

steam turbine, caused by more energy being rejected in thecondenser, especially operation modes 3, 9 and 12. For operationmode 3, with electric power selling and using wood chip as fuel, thecosts are high due to high fuel price, high fuel consumption, andhigh electric power consumption in the air condenser fans. Foroperation mode 9, with no electric power selling and using woodchip as fuel, the costs are high due to high fuel price, high electricpower consumption in the air condenser fans, and the low amountof electric power generated in the CHP plant. Finally, for operationmode 12, with no electric power selling and using charcoal as fuel,the high costs are due to the high electric power consumption inthe air condenser fans.

In Fig. 10 the total cost of production of electric power plus heat(flows 10 and 54 in Fig. 5) is correlated to the exergetic efficiency ofthe CHP plant for the several operation modes. It is noticeable thatthe total production costs have always the lower values for charcoalfuel, caused by its low price compared with wood chip. The totalproduction cost increases while the exergetic efficiency of the CHPplant decreases (Fig. 11). For electric power selling this behavior ismainly due to exergy destruction in the boiler and in the condenserwhile, for no electric power selling, the main cause is exergydestruction in the condenser.

5. Conclusions

For the operation modes assessed in this study, the turbinerequired for electric power selling is unsuitable for no electric po-wer selling. Increasing boiler feed water temperature improvesboiler efficiency, thus reducing fuel consumption in the RankineCycle. With electric power selling fuel consumption is increased,but also electric power generation efficiency and income. On theother hand, the energy utilization factor is low due to heat loss inthe condenser, as the flow from the low pressure turbine sectioninto the condenser is high. With no electric power selling, fuel flowis lower, the energy utilization factor is higher, due to lower heatloss in the condenser, and electric power generation efficiency islower, compared with the electric power selling condition. The useof an air cooled condenser increases auxiliary power consumptionin the operating conditions with high thermal load in thecondenser, applicable to operation modes with high electric powergeneration.

In the economic scenario considered implementation of the CHPplant using wood chips as fuel is not feasible. The feasibility of CHPplant implementation is achieved using charcoal as fuel, withbetter results obtained for 90% boiler efficiency and commerciali-zation of carbon credits. Charcoal is the most convenient fuel forelectric power selling, considering either future process upgrading

M.L.M. Rodrigues et al. / Applied Thermal Engineering 59 (2013) 174e181 181

or attractive electric power prices. The financial variables that mostinfluence the profitability of the small scale biomass CHP plantimplementation are price of electric power purchased, interest rateand capital investment. With minimummass flow extraction in thesteam turbine the steam amount flowing into the condenser in-creases, as well as electric power and heat costs, due to increasedirreversibility in the CHP plant. The operation modes with mini-mum mass flow extraction in the turbine are not feasible due tohigh costs. The minimum costs of electric power and heat wereattained using charcoal as fuel, considering no electric powerselling with maximum turbine steam extraction.

Acknowledgements

The authors thank FAPEMIG, for the financial support to thiswork. Thanks are also due to Rações Patense, ENGECROL and TGM,for the information supplied.

References

[1] L. Dong, H. Liu, S. Riffat, Development of small-scale and micro-scale biomass-fuelled CHP systems e a literature review, Appl. Therm. Eng. 29 (2009) 2119e2126.

[2] P.A. Filho, O. Bdar, Biomass source for energy in north-eastern Brazil, Appl.Energy 77 (2004) 51e67.

[3] E.S. Lora, R.V. Andrade, Biomass as energy source in Brazil, Renew. Sustain.Energy Rev. 13 (2009) 777e788.

[4] A. Al-Kassir, J. Gañan, A. Marcos, H. Olgun, Experimental study of gasificationof biomass residues for electrical energy generation, Int. J. Energy Res. 36(2012) 241e248.

[5] D. Vera, F. Jurado, K.D. Panopoulos, P. Grammelis, Modelling of biomassgasifier and microturbine for the olive oil industry, Int. J. Energy Res. 36 (2012)355e367.

[6] M. Preißinger, F. Heberle, D. Brüggemann, Thermodynamic analysis of double-stage biomass fired Organic Rankine Cycle for micro-cogeneration, Int. J. En-ergy Res. 36 (2012) 944e952.

[7] M. Loeser, M.A. Redfern, Modelling and simulation of a novel micro-scalecombined feedstock biomass generation plant for grid-independent powersupply, Int. J. Energy Res. 34 (2010) 303e320.

[8] J. Schmidt, S. Leduc, E. Dotzauer, G. Kindermann, E. Schmid, Potential ofbiomass-fired combined heat and power plants considering the spatial dis-tribution of biomass supply and heat demand, Int. J. Energy Res. 34 (2010)970e985.

[9] I. Vallios, T. Tsoutsos, G. Papadakis, Design of biomass district heating systems,Biomass Bioenergy 33 (2009) 659e678.

[10] H. Goodfellow, E. Tahti, Industrial Ventilation Design Guidebook, AcademicPress, San Diego, 2001.

[11] T. Savola, C. Fogelholm, Increased power to heat ratio of small scale CHPplants using biomass fuels and natural gas, Energy Convers. Manag. 47 (2006)3105e3118.

[12] Carbon Planet (Internet), Carbon Planet Ltd., Adelaide, c2000 (updated10.05.13, cited 11.05.13). Available from: http://www.carbonplanet.com.

[13] P. Schwarcz, M.A. Lozano, M.R. von Spakosvsky, A. Valero, Diagnostic analysisof PFBC power plant using a thermoeconomic methodology, in: Proc. ofTAIES’97 e Thermodynamic Analysis and Improvement of Energy SystemsInternational Conference, Beijing, 1997.

[14] A. Valero, L. Serra, M.A. Lozano, Structural theory of thermoeconomics, in:Proc. of 1993 ASME Advanced Energy System Division, San Diego, 1993.

[15] L. Serra, C.T. Cuadra, Structural theory of thermoeconomics, in:C.A. Frangopoulos (Ed.), Encyclopedia of Life Support Systems, EOLSS Pub-lishers, Oxford, 2006.