Unit 3.9 Steam

Unit 3.9 - Steam

©The Institute of Brewing & Distilling (Dipl. Brew 3 Revision Notes Version 1 September 2009)

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Unit 3.9 - Steam 3.9.1 Introduction Steam has been used extensively within breweries for heat and power for many years and is still the favoured choice for a number of reasons:

• It has a high latent heat

• Its heat can be released at temperatures ideal for beer processing (for example, wort boiling)

• It is cheap, being produced from water

• It is easily distributed throughout the brewery. Steam can also be used for motive power within the brewery, although this use is less common today, but in the days before distributed electricity, motive power for a brewery was provided by steam. A steam engine provided the power, which was distributed throughout the brewery by a system of drive shafts, pulleys and belts. Some breweries realised the energy saving principle of utilising the waste steam from the engine in the rest of the brewery. This is a concept now known as Combined Heat and Power or Co-generation and is one of the routes being promoted to reduce energy and carbon emissions liabilities. Several breweries retain their original power sources although more as a visitors attraction than a source of energy. Until recently two major UK breweries utilised steam power in the form of steam turbines generating electrical energy for use in the brewery. The steam leaving the turbine was used in the brewing process. Figure 3.9.1 shows a steam engine from the former Tolly Cobbold brewery in Ipswich.

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Figure 3.9.1 Steam engine at Tolly Cobbold brewery

Steam was also used to provide the power for the vehicles. Fortunately several of these remain, again as an attraction and to promote a brewery’s name when displayed at special functions. Figure 3.9.2 shows the Sentinel steam lorry owned by Shepherd Neame brewery in Faversham, Kent, UK. Figure 3.9.2 Sentinel steam lorry belonging to Shepherd Neame brewery

However the main use of steam today is for heating duties and it is on this use that is the primary focus of this section. Steam has some unique properties that make it the ideal choice for heating purposes

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Recap of Units important to the Use of Steam

Pressure is measured in pascals (Pa) but from convenience is often measured in bar. Note that ‘Absolute’ or ‘Gauge’ pressures may be used denoted by bara and barg

1 bar = 105 Pa Temperature is measured in kelvin (K), but is more often measured in degrees celcius (°C). This is perfectly acceptable for the majority of heat calculations. Specific Heat is measured in kJ kg-1 K-1 Enthalpy or more correctly specific Enthalpy is the heat content per unit mass of the material at a given temperature and is measured in kJ kg-1 Latent heat associated with a phase change is measured in kJ kg-1

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3.9.2 Properties Ice, Water and Steam Water cab exist in three forms:

• Solid - Ice

• Liquid - Water

• Vapour - Steam The temperature at which all 3 forms of water coexist is referred to as the triple point. This occurs at 0.01°C. Move either way on the temperature scale, and the coexisting states are reduced to just two. It is this triple point which is used to define the S.I. unit of temperature namely the kelvin. The temperature at which water changes to steam will depend on the pressure. This is given by the vapour - liquid equilibrium curve as shown in Figure 3.9.3. Note that at 1.01325 bara, the equilibrium temperature is 100°C. At 10 bara , which is the pressure commonly used for brewery steam systems, the equilibrium temperature is 179.9°C. The energy needed to change unit mass from liquid to vapour is termed the Latent Heat. This is heat associated with the phase change only. Figure 3.9.3 Vapour liquid equilibrium for water

0 5 10 15 20

Pressure bar absolute

0

50

100

150

200

250

Temperature °C

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The thermodynamic data for steam and water can be found in data tables referred to as Steam tables, (see Table 3.9.1). One convenient graphical presentation of the physical properties of steam plots the absolute pressure against the specific enthalpy for the liquid and vapour phases. This is known as a Mollier Chart. This type of chart is also used to describe the refrigeration cycle (see Section 3.10.3). Figure 3.9.4 shows a Mollier chart for steam over the pressure range 0 to 221.2 bara . Note that the maxima is the critical point at 221.2 bara and a temperature of 374.15 °C. The enthalpy of saturated liquid is shown by the left hand line and the saturated vapour by the right hand line. The difference in enthalpy between these 2 lines at a given pressure, is the Latent Heat. At the critical point, there is no difference between the liquid and vapour enthalpies, i.e. there is no latent heat.

Figure 3.9.4 Mollier Chart for Steam: full range

0 500 1000 1500 2000 2500 3000 3500

Specific enthalpy kJ/kg

0

50

100

150

200

250


The majority of brewery systems will operate below 20 bara. and therefore the question of criticality need be of little concern. Figure 3.9.5 shows a section of the Mollier chart covering the pressure range 0 to 20 bara. This chart also shows the isotherms for temperatures from 50°C to 200°. These are shown by the yellow lines.

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Figure 3.9.5 Mollier Chart for steam in the range 0 to 20 bara

0 500 1000 1500 2000 2500 3000 3500

Specific enthalpy kJ/kg

0

5

10

15

20


Superheated

vapour

Liquid to vapour transitionSaturated liquid

Saturated vapour

200°C

150°C

100°C50°C

Liquid phase

The Mollier chart can be used to explain the effects resulting from adding energy to water in the liquid phase. For example if water at 50°C and 5 bara and an enthalpy of 209.2 kJ kg-1 is heated, the first effect is an increase in the temperature. This is referred to as adding sensible heat. On the Mollier chart, this is shown by a horizontal line crossing of the temperature isotherms. Adding more heat results in raising the temperature until at 151.8°C and an enthalpy of 640.1 kJ kg-1, the point is reached when the first bubble of vapour appears. In this condition, the water is referred to as saturated liquid and is represented by a point on the (red) saturated liquid line at 5 bar. Adding more heat results in more liquid being converted to vapour. This process occurs at constant pressure (isobaric) and constant temperature (isothermal). The process continues until a point is reached on the saturated vapour line when the last drop of liquid is converted to vapour. At this point the enthalpy is 2747.5 kJ kg-1. The difference in Specific Enthalpy between the saturated liquid and saturated vapour lines is the Latent heat at the given pressure. Under these conditions the Latent Heat is 2107.4 kJ kg-1 (that is, 2747.5 - 640.1 = 2107.4). Adding heat to saturated vapour at constant pressure, results in a superheated vapour i.e. heated beyond its equilibrium temperature. This is shown on the Mollier chart by a crossing of the isotherms in the vapour phase. In this state the steam behaves as any other gas.

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Some definition of terms Saturated liquid: Liquid which is in equilibrium with its vapour. Saturated steam: Steam. which is in equilibrium with water such that the slightest loss of energy causes liquid water to form. Wet saturated steam: Saturated steam which contains liquid water. Dry saturated steam: Saturated steam which contains no liquid water. In practice, dry saturated steam is difficult to achieve. Superheated steam: Steam which has been heated to beyond its saturation temperature (at a defined pressure). Sensible heat: Heat energy which causes a measurable temperature rise. Specific Heat: The heat needed to raise the temperature of 1 kg through 1K temperature change. Latent heat of vaporisation: The heat energy needed to change the phase of 1 kg from liquid to vapour. Specific Enthalpy: The heat content in kJ/kg of the water or steam at a given temperature and pressure.

Superheated steam vs saturated steam Superheated steam is a stable vapour. The transfer of sensible heat from all vapours is very poor, being the basic properties of a gas (see Section 3.8.3 Heat Transfer - Conductivity). For this reason, superheated steam is not used in factories, such as breweries, where the steam is being used as a heat transfer medium. Superheated steam is of importance in power generation applications, for example steam turbine driven power stations. For heat transfer applications, use is made of the excellent heat transfer performance of condensing steam, so dry saturated steam is required. Super-heated steam is not suitable for heat transfer purposes. Steam quality is a term used to describe the amount of free moisture in the steam. Clean Steam has been a requirement of the pharmaceutical industry and is becoming a requirement of the food and beverage industries. Clean steam is steam generated from deionised water in high quality equipment, usually using ‘utility steam’ as the heating medium. Clean steam is sometimes required where it is likely to be in contact with the product, for example in keg sterilisation, where there needs to be an assurance of freedom from any chemical additives.

Steam Tables The thermodynamic data for steam and water is available in Steam Tables. Table 3.9.1 shows an extract from the steam tables although the reader is referred to an actual published table for more complete data. It should be noted that tables from different sources may use different units for the measurement of pressure and for temperature.

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Table 3.9.1 Extract from the Tables for Saturated Water and Steam

Pressure Temperature Specific Volume

Specific Enthalpy

Specific Enthalpy

Specific Enthalpy

bara °C m³/kg Water kJ/kg Evaporation kJ/kg

Vapour kJ/kg

0.474 80.0 3.410 335.1 2308.7 2643.8 0.700 90.0 2.360 376.8 2283.3 2660.1

1.01325 100.0 1.673 419.1 2256.9 2676.0 2.00 120.2 0.885 504.7 2201.6 2706.3 3.00 133.5 0.606 561.4 2163.3 2724.7 4.00 143.6 0.462 604.7 2133.0 2737.6 5.00 151.8 0.375 640.1 2107.4 2747.5 6.00 158.8 0.315 670.4 2085.0 2755.5 8.00 170.4 0.240 720.9 2046.5 2767.5 10.00 179.9 0.194 762.6 2013.6 2776.2 15.00 188.0 0.132 844.7 1945.2 2789.9 20.00 212.4 0.099 908.6 1888.6 2797.2

The column titled Specific Volume is the volume occupied by 1kg of steam at a given pressure and temperature. It is of use when sizing steam pipe-work systems. The ‘Specific Enthalpy Evaporation’ is the difference between the Specific Enthalpy of the vapour and liquid states and is equal to the Latent Heat. Steam tables are very useful for calculating heat loads in water/ steam systems. Since specific heat varies with temperature, calculating heat loads involving sensible heat in addition to latent heat, could be onerous, but this information is already incorporated into the property data of steam tables. Note that when calculating heat loads with water or steam systems, an alternative to using the specific heat and temperature difference, is to use the difference of the enthalpies at the two temperatures. This is demonstrated in the example 3.9.1. (below):

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Example 3.9.1 Calculate the total amount of steam and the average steam flow rate required when heating a brewery copper containing 500hl of wort from 80°C to boiling temperature in 30 minutes followed by a 90 minute boil with a total evaporation of 7.5% of the initial copper volume. Assume the physical properties of wort are the same as water. Steam is available for the copper at 3 bara. The steam data is in Table 3.9.1

Wort heating

Volume of wort = 500/10 m³ = 50m³ Density of wort = 1000 kg m-3

Mass of wort = 50 * 1000 kg = 50000 kg

Enthalpy of wort at start = 50000 * 335.1

= 16755000 kJ

Enthalpy after heating = 50000 * 419.1

= 20955000 kJ

Enthalpy difference = 4200000 kJ

Steam heat release = m * (2724.7 - 561.4) = m * 2163.3 kJ

By a heat balance 4200000 kJ = m * 2163.3 kJ

Steam mass required m = 4200000/2163.3 = 1941.5 kg

Steam flow rate = 1941.5 * 60/30

= 3882.9 kg/h

Wort boiling

Mass of wort = 50000 kg

Mass evaporated = 50000 * 7.5/100

= 3750 kg

Heat required = 3750 * (2676 – 419.1) kJ

= 3750 * 2256.9

= 8463375 kJ

By heat balance

8463375 kJ = m * 2163.3 kJ

Steam mass required m = 8463375/2163.3

m = 3912.3 kg

Steam flow rate = 3912.3 *60/90

= 2608.2 kg/h

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3.9.2 Steam Systems All graphics in this section are by courtesy of Spirax Sarco unless otherwise stated

Introduction In brewery systems, steam is generated in a boiler and it is usual to design the system to meet the peak steam demand. Generally, the steam is raised at a pressure of 10 – 15 bar for distribution. The steam generated in the boiler is often passed to a steam accumulator, so that there is buffer capacity available at times of high steam demand \9e.g. when a wort boiler comes on-line). It is also common for breweries to be equipped with more than one boiler, again to meet peak demand, but also to allow for maintenance and breakdowns. Steam Generation Steam is generated in a boiler. The type of boiler commonly in use is referred to as a ‘fire tube’ or ‘shell boiler’, (see Figure 3.9.6). Figure 3.9.6 Section of a shell boiler

The boiler is comprised of a large welded steel shell, usually circular in cross section. Set into this shell is one (or possibly two) ‘furnace tubes’, approximately 1m diameter in which the combustion of the fuel takes place. At the end of the furnace tube, the hot combustion gases reverse in direction and pass through a series of tubes of approximately 50 mm diameter to the front of the boiler, where their direction is again reversed to pass back through a series of 50 mm diameter tubes and into the flue system at the rear of the boiler. Water fills the shell to a level just above the top row of tubes. Above this is the ‘steam space’ which acts as a small reserve of steam and a space where any water droplets can separate from the steam. It is essential to maintain the

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water level above these tubes in order to prevent them overheating and possible failure resulting from oxidation of the tube metal. The boiler is fitted with a relief valve to prevent excessive pressure occurring in the boiler, even under the worst imaginable conditions, for example the burner controls malfunctioning in the fully open position. The boiler is also fitted with level controls to operate the admission of feed-water, to give warning (alarm), then boiler shut-down, in the event of either excessive or insufficient level. A ‘gauge glass’ and pressure gauge give visual indication of the boiler level and steam pressure. Heat is transferred in the combustion tube, by a combination of radiation and convection. However, in the smaller diameter tubes, combustion has been completed and the transfer of heat is by convection only. Flue gases leave the boiler at a temperature of between 10 to 15°C above that of the steam in the boiler. Scaling on the water-side and fouling on the ‘fire-side’ can cause this temperature difference to increase and thereby reduce the boiler efficiency. When firing on natural gas, it is possible to fit an additional heat exchanger into the flue system to extract more heat out of flue gases to pre-heat the incoming feed-water. This is known as an ‘economiser’. Because of the sulphur content of oil fuels, economisers cannot be used since there is a risk of forming highly acidic, hence corrosive condensates in the flue system Steam distribution Steam is distributed throughout the brewery by a pipe-work system. The pressure selected is typically in the range 6 to 10 bar. A general rule is that the system is designed for a maximum steam velocity of 25 m/s. The choice of pipe sizes is a balance between high pressures (hence lower density) and smaller pipes, but at reduced boiler efficiencies and lower pressures (hence larger pipe sizes), but at increased boiler efficiencies. System features A properly designed steam distribution system may or may not require the inclusion of a steam accumulator, but will have the following features:

• Steam pipes sized for a maximum velocity of 25 m s-1.

• Steam pipes well insulated to minimise heat losses

• Steam pipes should slope approximately 1 in 100 to carry any condensate with the flow to a collection point. Vertical runs should be used where an increase in height is required.

• Condensate collection points should be provided in horizontal runs of pipe and at the base of vertical runs.

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• Condensate is valuable for its quality as boiler feed-water and its heat content. Its recovery must be maximised.

• Long straight runs of pipe (over 25 m) must be fitted with expansion facilities either as an expansion loop or by bellows. Where only short straight runs between bends exist, sufficient flexibility can be gained from the bends although the pipe supports must be designed to accommodate movement.

• Where steam at a pressure lower than the supply pressure is required, then a pressure reducing station must be provided.

• Pressure relief valves must be installed to protect equipment from a pressure greater than its design pressure, in the event of a malfunction.

Condensate Removal and Steam Traps

As heat is lost from the steam system, condensation occurs. If not removed, condensate could cause damage to the steam system on account of the kinetic energy of the water travelling at up to 25 m s-1. The effect of ‘plugs’ of condensate hitting valves and fittings can be heard as ‘hammer’ in the pipes. This may cause the pipes to move violently so damaging the pipes and their supports. In steam heated equipment the presence of condensate has the effect of covering part of the heat transfer area, an effect known as ‘blinding’ or ‘blanketing’. The purpose of a steam trap is to allow condensate to flow out of the steam system whilst retaining the steam. Figure 3.9.7 shows the mechanism by which ‘slugs’ of condensate can form in a steam distribution system. Figure 3.9.7 Formation of condensate ‘slugs’

Condensate may be removed from pipe-work by providing collection points as shown in Figure 3.9.98 A similar facility would form the base of a vertical run of pipe.

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Figure 3.9.8 Condensate Collection

Condensate forms as small droplets suspended in the steam. Often, before sensitive items of equipment such as instruments, it is necessary to remove these droplets. This is achieved by a steam separator. The steam flows over a series of baffles on which the condensate collects. Figure 3.9.9 shows one particular design of steam separator. Figure 3.9.9 Steam Separator

Figure 3.9.10 shows several different styles of separators

Figure 3.9.10 Various Styles of Steam Separator

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Condensate collected by the separator must be removed from the system. Likewise condensate forming in equipment, must also be removed. If condensate were allowed to accumulate in the equipment, it would effectively obscure part or all of the heat transfer area and so reduce the effectiveness of the equipment. Steam traps are used to allow the flow of condensate but prevent steam from escaping from the equipment. Figure 3.9.11 shows the external view of a float trap

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Figure 3.9.11 Float Trap

The float trap comprises of a chamber containing a small float. As condensate collects in the chamber, the float rises and opens the condensate valve to drain the condensate from the valve. As the level falls, the valve closes to prevent the passage of steam. Figure 3.9.12 shows the operation of this type of trap. Figure 3.9.12 Operation of the Float Trap

There are several different types of steam trap for various applications. One type incorporates a large collection chamber which may be used to pump condensate to the boiler-house by an application of steam pressure. This is the ‘pumping steam trap as shown in Figure 3.9.13.

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Figure 3.9.13 Pumping Steam Trap

Condensate is collected locally in condensate collection sets, which comprise of a tank fitted with level switches and a pump. The pump operates in response to the switches to return condensate to the boiler-house. Figure 3.9.14 shows a typical condensate collection tank.

Figure 3.9.14 A Condensate Collection Tank

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The Value of Condensate Condensate is a valuable source of boiler feed-water. Firstly, it is good quality water which needs little further treatment (other than filtration to remove any corrosion products that may have been picked up) before feeding to the boiler. Therefore recovering condensate represents a saving in water, and its reatment cost as effluent, if wasted to drain. Secondly, condensate has a valuable heat content. Returning hot condensate to the boiler reduces the energy needed to raise the water to boiling temperature. Reducing Valve A reducing valve is a valve, which automatically reduces the pressure of the steam for distribution to, for example, a brewery kettle, which can only accept steam at below the distribution pressure. Various systems exist. One common type is the pilot operated valve, shown in Figure 3.9.15. In these valves, the pressure downstream of the valve is applied to a diaphragm and the force is balanced against the spring force; representing the setting on the valve. Any imbalance causes a steam pressure to be applied to the valve to adjust the opening in order to restore the balance.

Figure 3.9.15 Pilot Operated Valve

Alternatively, the pressure reduction may be achieved by a conventional pressure sensor, controller and control valve. This system has the advantage that the pressure may be varied easily from a control panel or via the computer

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control link. Figure 3.9.16 shows the 3 components, namely: pressure sensor, process controller, control valve. Figure 3.9.16 Components of a Process Control - based Pressure Reduction System

Figure 3.9.17 shows a correctly designed ‘reducing station’ for reducing the pressure of the steam. Figure 3.9.17 A Pressure ‘Reducing Station’

The key features are (in the direction of the steam flow),

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1) Condensate separator and removal point to remove condensate droplets which otherwise could damage the reducing valve.

2) Isolation valve to permit isolation for maintenance of the reducing valve. 3) Strainer to prevent solid particles from entering the pressure reducing

valve. 4) Inlet pressure gauge. 5) Reducing valve. The type shown is the pilot operated type. 6) Relief Valve. This valve is sized to pass the full flow of the reducing

valve should it fail fully open and prevent the pressure downstream exceeding the designed pressure.

7) Outlet pressure gauge. 8) Isolation valve. Pressure Relief Valve A pressure relief valve is an item essential for safety. The function of the relief valve is to open and vent excessive steam pressure from a system to avoid subjecting the equipment to an excessive pressure. A typical application would be after a pressure reducing station supplying jacketed vessels with steam. Typically jacketed vessels have a designed pressure of approximately 2 bar and are likely to fail if subjected to steam at the full distribution pressure. The function of the relief valve to vent excess pressure in the event of a failure of the reducing set. It is assumed that the reducing set would fail in the fully open condition. Relief valves must be designed for the most extreme of conditions to ensure the safety of the plant. Figure 3.9.18 shows an external view of a relief valve. This type of valve operates by a balance between the steam pressure force being balanced against a spring force. The setting on the spring is adjustable to give the required opening pressure. Once set, the cover over the spring adjuster should be locked or sealed. The red lever on the top of the valve is a lifting lever to open the valve to check for freedom of movement. It is obligatory for pressure relief valves to be inspected and tested at approved intervals (typically every 2 years) under the pressure systems regulations.

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Figure 3.9.18 External View of Relief Valves

Figure 3.9.19 shows a sectioned view of a relief valve showing the adjustment spring, and seating arrangement.

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Figure 3.9.19 Sectioned View of a Relief Valve

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Vacuum Breaking Valves

A problem with operating steam jacketed vessels is that on cooling, a near perfect vacuum can be created in the jacket. If not ‘broken’ this vacuum could cause a collapse of the jacket. A vacuum can be ‘broken’ by fitting a small non-return valve, which allows air to enter the jacket when a slight depression in pressure occurs. Figure 3.9.20 shows the operation of vacuum breaker valves. Figure 3.9.20 Vacuum breaker valves

Air Vents On starting a steam heated system, it is likely that air has entered the system, either intentionally via the vacuum breaker valves or by leakage. If not removed, the air effectively ‘dilutes’ the steam and hinders heat transfer. Air vent valves operate by having a small temperature sensitive element, which allows the valve to open when exposed to the air but close when exposed to steam. Often air vent valves may be seen on external wort boilers and may be seen to emit a small amount of steam at the start of a boil but close once the air has been expelled. Figure 3.9.21 shows an air vent valve Figure 3.9.21 Sectioned view of Air Vent Valve

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Steam Metering Steam metering is necessary from both an energy management and a process control aspect. Various methods of metering have been developed. One of the first steam meters was based on the orifice plate. A plate with an orifice of accurately known diameter is mounted in the pipe carrying the steam. The steam flow generates a pressure loss across the plate which is measured by a differential pressure sensor. Early types were based on a column of mercury but these have been displaced by differential pressure sensors based on the strain gauge principle. The orifice plate types suffer a major disadvantage that the relationship between the differential pressure and the flow is not linear but a ‘square law’. This means that ‘range or turndown’ of this form of measurement is limited to approximately 4:1. The turndown is the ratio of the maximum to minimum flow which can be measured. Figure 3.9.22 shows a typical orifice plate in a manufactured ‘carrier’ complete with pressure tapping. This plate and carrier assembly is located between flanges in the pipe-work. Figure 3.9.22 Orifice Plate and Sectioned Carrier

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Figure 3.9.23 shows the arrangement connecting the orifice plate with the pressure sensor. Note that the sensor is below the level of the orifice plate. The connecting lines are designed to operate full of condensate.

Figure 3.9.23 Connection of Orifice Plate to Pressure Sensor

A recent improvement to the simple orifice is the ‘variable area meter’ . In this form of meter, the steam flows past a spring-loaded plug in an orifice. As the flow increases so does the area by virtue of movement of the plug. The plugs are machined to a shape such that the pressure differential against flow characteristic, is almost linear. The pressure differential is sensed by a differential pressure sensor as used with the orifice plate. In Figure 3.9.24, this differential pressure sensor forms part of the meter assembly. The meter shown in Figure 3.9.24 features a local display to give local indication of the flow. Generally, the signal from these meters would be transmitted to a control panel or central data collection point.

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Because of this linear characteristic, variable area meters have a good turndown ratio of 40:1. Figure 3.9.24 shows the exterior view of the variable area meter. Figure 3.9.24 Variable Area Meter

Figure 3.9.25 shows a cross section view of the variable area meter.

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Figure 3.9.25 Cross Section of the Variable Area Meter

By combining the measurements of flow with measurements of the pressure and temperature, it is possible to calculate the mass flow. This is achieved by inline electronics. Vortex Meters An alternative to pressure differential is the principle of vortex measurement. As a fluid passes around a blunt shape, vortices are generated: the frequency of which is proportional to the flow. The frequency of the vibrations is detected and converted to a signal for transmission to a central control panel. Figure 3.9.26 shows a typical vortex meter.

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Figure 3.9.26 Vortex meter

(photograph Endress & Hauser)

The bluff body, which generates the vortices can be seen to the right of the metering head. The sensors are located in line with the sensor and electronics housing in blue. Safety All steam systems are classified under the European wide regulations covering the design and use of pressurised vapour systems. These regulations place responsibility for safe operation of such systems with the operator of the plant. In essence, these regulations make obligatory the maintenance, testing and inspection of such systems to be to an agreed programme. Normally, the interval for the inspection and testing is agreed with the operating company’s insurers. A crucial feature of the legislation is the need to keep comprehensive records of all work undertaken on the system. Boilers need to be shut-down for a full inspection by an authorised inspector every 14 months. This inspection will include the safety equipment such as the relief valves, level switches and pressure indicators as well as the physical condition of the boiler. All steam pipework and equipment are also all subject to the same safety inspection requirements.

Unit 3.9 Steam

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