The Performance of a Double Effect Calorimeter - Research Paper Example

UO 26 DOUBLE EFFECT FALLING FILM EVAPORATOR Summary The overall aim of this experiment was to evaluate the performance of a double effect calorimeter. Mass balance equation in calculating the evaporation rates in the evaporators. It was established from the experiment that there is an inverse relationship between the two quantities where the economy reduces linearly with flow rate. At a feed flow rate of 6kg/s the economy was found to be 131.67 and this reduced to 122.12% as the flow rate was increased to 6.55%. The conclusion was that an increase in the product produced can only be increased if there a proportional increase in steam flow rate. From the experiment it was established that an increase in steam flow rate resulted in an increase in economy of evaporator but this increase in economy reduced as the steam flow rate increased with the conclusion from this being that beyond a certain flow rate increase in steam flow rate was uneconomical. A decease the pressure level resulted in increased economy and reduced temperature and this was seen to be the solution of concentrating solutions which are likely to be denatured at high temperatures. The error in amount of evaporation experience in first effect calculated and was found to be 11% with the actual error being 0.013 kg. It was concluded that the errors were within acceptable range. Table of contents Summary ii Table of contents iii 1.0 Introduction 1 1.1 Aims 1 1.2 Theory 1 1.2.1 Forward feed 2 1.3 Mass balance calculation 3 1.4 Performance of evaporators (capacity and economy) 4 3.0 Methodology 5 3.1 Apparatus 5 3. 2 Operating procedure 6 3.2.1 Start Up 7 3.2.2 Operations 8 4.0 Results 9 4.1 Relationship between economy and feed flow rate QF 9 4.2 Relationship between economy and steam flow rate QS 10 4.3 Relationship between economy and pressure 12 4.4 Error analysis 13 5.0 Discussion 15 5.1 Conclusion 16 References 18 APPENDIX 1: Variation between of feed flow rate and economy 21 APPENDIX 2 Variation of steam flow rate with economy 21 APPENDIX 3: Variation of pressure and economy 23 APPENDIX 4 25 APPENDIX 5 26 1.0 Introduction Evaporation is a process involving the removal of solvent as vapour from a solution, slurry or where solids are suspended in a liquid. This aims at concentrating a non-volatile solute, which could be an organic compound, acids/bases, and inorganic salts from solvents. Some of the common solutes are sodium sulfate, caustic soda, phosphoric acid, sodium chloride, caustic potash and urea. Water is the commonly used solvent in evaporation systems1. There is a distinct difference between evaporation and other processes such as drying and distillation. For the case of distillation, there is separation of the components in the solution depending on their distribution in their vapour phase and liquid phase . Drying on the other hand involves moisture being removed from a substance by exposure of the substance to a stream of hot gases that carries away the moisture with solid residue being left. In evaporation process, there is stoppage of evaporation before precipitation of solutes starts. 1.1 Aims 1. To study the effects of variable steam flow rate on evaporator performance. 2. To study the effects of variable feed flow rate on evaporator performance. . 3. To study the effect of operating under vacuum on evaporator performance. . 4. To practice standard procedures for validation of data collection and processing. 5. To perform mass and energy balances over sections and the complete unit. (TBA with staff) 1.2 Theory The number of effects are used to classify evaporators. In a single effect evaporator there is condensation of vapour generated upon heating of the feed water and the more concentrated product is drawn at the bottom of the evaporator. In the single effect, there is simplification of operation but the efficiency at which steam is put into use is low, with the evaporation of 1kg of water needing 1.1 to 1.3kg steam. The vapour generated per unit steam consumed can be improved through addition of the number of evaporators, where the evaporators are put in series such that the steam from one evaporator is the source of heat in subsequent evaporator. In a case involving the steam generated from the second generator being condensed the arrangement result to what is referred to as double effect evaporator (what is being dealt with in this experiment). In a double effect evaporator the amount of water evaporated is almost twice that involved in the single effect for the same amount of steam. There can be additional effects such that we can have triple effect for three evaporator in series; quadruple effect for the case of four evaporators. The number of evaporators can be increased up to 7 beyond which it becomes uneconomical2. Depending on the feeding arrangement there can a number of configuration including; forward feed, backward feed, mixed feed and parallel feed. In this case we are dealing with forward deed and it is discussed further under the next. 1.2.1 Forward feed Forward feeding can be thought of as being the typical feeding method as far as multi-effect evaporators are concerned. Under this configuration there is introduction of steam in the first evaporator with the feed being passed from effect to the next parallel to the vapour from preceding effect. With this type of arrangement there is an increase in concentration as the feed move along the evaporators6. This type of feeding find application in cases where the resulting concentrated product is likely to degenerate when exposed to high level of temperatures. The withdrawal of the product happens in the last evaporator in the series and a pump is needed for pumping the feed to the first effect. A pump is also needed for removal of the concentrated product from the last effect. For movement of the product in the middle effects, a pump may not be necessary bearing in mind that that there is flow from high pressure region to lower pressure region. 1.3 Mass balance calculation First effect = 0 and therefore =0 In this equation  = the total amount of heat transferred in 1st effect  = the rate of steam supplied in 1st effect  =latent heat of steam supplied in 1st effect  =the feed flow rate =specific heat of water  =the feed temperature  =rate of vapour generated in 1st effect = temperature of steam condensing in 1st effect = final temperature of steam in 1st effect = latent heat of steam condensing in 1st effect Second effect  and therefore   = the total amount of heat transferred in 2nd effect  = the rate of steam generated in 1st effect  = latent heat of steam condensing in 1st effect  =the feed flow rate  = temperature of steam condensing in 2nd effect  =rate of vapour generated in 2nd effect = temperature of steam condensing in 1st effect = final temperature of steam in 2nd effect  = latent heat of steam condensing in 2nd effect 1.4 Performance of evaporators (capacity and economy) Capacity and economy are the two quantities used in measurement of performance in steam heated evaporator. Capacity simply gives the mass in kg of water that is vapourized in one hour. Economy on the other hand gives the mass in kg of the water vapourized as the feed passes through all the effects for each kilogram of steam consumed. In case of a single effect the economy about 0.8 (cannot go beyond 1). In a multi-effect evaporator with n effects the capacity will be n-times the capacity of a single effect evaporator while the economy will be equal to about 0.8n4. It is should be noted however, increasing the number of effects come with an increase in pumps, pipe work and valves which brings about an increase in operating costs and equipment. Calculation of economy Economy =  Where the variables are as described in the second effect equation 3.0 Methodology 3.1 Apparatus P1-Metering pump in stainless steel AISI 316, 0-18L/hr @ 2 bar P2 Liquid ring vacuum pump TK5 Air-water separator for vacuum pump, stainless steel AISI 304 TK1 Feed tank in borosilicate glass, capacity of 25 litres TK2 Collection tank for the concentrated product in borosilicate glass, capacity 10 litres TK4 Graduated borosilicate glass collection tank for the condensed steam, capacity of 1 litre SC Steam trap in stainless steel AISI 304 E1 Falling-film evaporator, stainless steel AISI 316 execution on the tube side and stainless steel AISI 304 on the shell side, exchange surface of 0.27m2 E2 Shell-and-tube condenser, stainless steel AISI 316 on the tube side and stainless steel AISI 304 on the shell side, exchange surface of 1.1m2 E3 Tube-tube heat exchanger in stainless steel AISI 304 PI1,PI2 2 Bourdon pressure gages, range 0,6 bar PI3 Bourdon pressure gage, range of 0, 1.6 PI4 Bourdon vacuum gage, range of 0,-1 bar FT1 Steam flow rate transmitter, differential pressure type, stainless steel AISI 316, range 0 ton 1000 mmH2O, output signal of 4 to 20Ma proportional to 0,15 kg/h of steam at 4 bar Calibrated orifice for steam flow rate measurement to the first level evaporator FV1 Steam flow rate pneumatic control valve, stainless steel AISI 316 execution, Cv=0.32 TI1 to TI12 12 RTDs Pt100, with sheath of stainless steel AISI 316 12 electronic temperature indicators, range 0,200  LT1 First effect level transmitter, capacitance type, range 0,300 mmmH2O PT4 Absolute pressure transmitter, stainless steel AISI 316 execution, range 0,1000 mBar EV1 Vacuum pump solenoid valve Electric switchboard, protection level IP 55, with synoptic of the plant and E.L.C.B. Figure 3.1 3. 2 Operating procedure The evaporator is instrumented for direct readout of temperatures and pressures. Flowrates are manually measured. When making adjustment to steam flow rate it was important that gloves be worn 3.2.1 Start Up At the start it was ensured that all the manual valves were in a closed position, and then valves V1, V5, V13, V15, V17, and V18 were to be opened, with subsequent procedure involving partial opening of valve V11, V12, V21, and V22. After the opening of these valves the power was switched on followed by the opening of mains water supply valve. The compressed air supply valve was then opened , where the maximum pressure is 6 bar and a maximum consumption of 5m3/hr. there was adjustment of V11 so as to set the cooling water flow rate F12 directed to the condenser E3 at approximately 150l/hr . The next step was to enable E.L.C.B and the start button on the contro9l button was opened. TK1 was filled to 90% while FV1 was closed fully by use of pressure reducer MC3 steam control. P2 was started followed by P1 by switching to 1, with the feed flow rate P1 being adjusted to 50% by use of pressure reducer MC1 feed control on the switch board. The residual pressure at P14 was set to -0.8 bars, by use of V12, with closure of valve resulting to an increase in vacuum. While making this adjustment, failure in achieving the vacuum desired meant that there was leakage and this was to be overcome all pipe connections and fittings being rechecked. The mains steam valve was opened by staff through opening of V4 was opened, then there was adjustment of FV1 to 7.5kg/h which is 50% steam flow rate. LT1 was allowed to rise to approximately 40%, then the flow rate was adjusted (pump P1) by use of the MC2 level controller to maintain it level. Temperature TI11 was observation, and if it was to high flow rate was increased to condenser through adjustments of V11. 3.2.2 Operations There was continuous checking of LT1 as the experiment progressed and with the unit heating this resulted to a drop in the level. By balancing of P1 and P2 it was possible to maintain the set point at 40%. Draining of TK2 involved closing of V13, V15, open V14, V16 and upon being emptied, V14 and V16 were closed while V15 was opened at a slow rate up to a point when stability in pressure was achieved , after which V13 was opened. Draining of TK3 involved closure of V17 and V18 then opening V19 and V20. Reopening of TK3 involved closing V19 AND V20 and slowly opening of V18 until a point is reached there is stability in pressure, it is at this point when there can be opening of V17. The experiment involved constant checking the level of TK4 and TK5, and V8 and V9 respectively were used in draining when it was necessary. 4.0 Results In this section the results of the experiment have been given. The results have been presented under the following subheadings: relationship between economy and feed flow rate; economy and steam flow rate QS and economy and pressure. Also error analysis is addressed in this section. 4.1 Relationship between economy and feed flow rate QF In order to establish the relationship between economy and change in feed flow rate , the steam flow rate was kept constant at 0.5kg/s while varying feed flow rate. Table 3.1 gives the pattern of change between feed flow rate and economy. Also in the table the relationship between flow rate and vapour evaporation in first effect D1 and evaporation in second flow rate D2 have been given. In the table it can be observed that at a feed flow rate of 6kg/s the economy is 131.67% and when the feed flow rate is increased to 6.55 kg/s the economy is reduced to 122.12%. The relationship between economy and feed flow rate is as shown in figure 3.1 graphically. From the figure it can be seen that there is an inverse relationship between the two quantities where the economy reduces linearly with flow rate. This is an indication that increasing the feed flow rate will result to a reduction in the amount of the feed flow that will be evaporated. Table 4.1 wf D1 D2 Econ 6 0.13 0.54 134.78 6.05 0.13 0.54 133.63 6.1 0.13 0.54 132.48 6.15 0.12 0.53 131.33 6.2 0.12 0.53 130.18 6.25 0.12 0.53 129.03 6.3 0.11 0.52 127.88 6.35 0.11 0.52 126.73 6.4 0.11 0.52 125.58 6.45 0.11 0.52 124.43 6.5 0.10 0.51 123.27 6.55 0.10 0.51 122.12 Figure 4.1: Relationship between economy and feed flow rate QF 4.2 Relationship between economy and steam flow rate QS Table 3.2 gives the pattern of change between steam flow rate and the economy. Also in the table the relationship between flow rate and vapour evaporation in first effect D1 and evaporation in second flow rate D2 have been given. Figure 3.1 from the table it can be seen that at a flow rate of o.5kg/s the economy is 131.67% and when the flow rate is increased to 1.05kg/s the economy is increased to 163.15% gives the relationship between steam flow rate and the economy. Figure 3.2 gives the relationship between the variables diagrammatically. It can be observed from the graph that an increase in the steam flow rate results to an increase in economy. It can be seen from the graph that the graph seems to start flattening with a further increase in steam flow rate. Table 4.2 Do D1 D2 Econ 0.5 0.12 0.53 131.67 0.55 0.17 0.58 137.14 0.6 0.22 0.63 141.69 0.65 0.27 0.68 145.54 0.7 0.31 0.73 148.84 0.75 0.36 0.78 151.71 0.8 0.41 0.83 154.21 0.85 0.45 0.88 156.42 0.9 0.50 0.93 158.38 0.95 0.55 0.97 160.14 1 0.59 1.02 161.72 1.05 0.64 1.07 163.15 Figure 3.2: Relationship between economy and steam flow rate QS 4.3 Relationship between economy and pressure In order to increase the rate of evaporation the negative pressure is to be provided in the evaporators. Table 3.3 gives the result of change in pressure and economy. Also in the table the relationship between pressure and vapour evaporation in first effect D1 and evaporation in second flow rate D2 have been given. From the table it can be seen that at a pressure of 0.01bar we have economy of 363.68% and when pressure is increased to 0.02 bar there is a reduction in economy to 135.66. The graphical presentation of relationship between the economy and pressure is as shown in figure 3.3. From the figure it can be seen that the economy is much sensitive to pressure (negative pressure) and as the pressure increases in the evaporator the sensitivity is seen to reduce. Table 3.3: press D1 D2 Econ 0.01 0.67 1.14 363.68 0.02 0.57 1.03 319.32 0.03 0.51 0.95 291.27 0.04 0.46 0.90 270.33 0.05 0.42 0.85 253.61 0.06 0.38 0.81 239.40 0.07 0.35 0.78 227.32 0.08 0.33 0.75 216.51 0.09 0.30 0.73 206.53 0.10 0.23 0.71 186.46 0.15 0.20 0.61 162.04 0.20 0.13 0.54 135.66 4.4 Error analysis Error analysis is important in understanding of reliability of the data obtained directly from the experiment and those derived by application of some equations. This section involves use of some equation in calculation of the errors. In the calculation of calculation of heat gained by the feed water as in upon entry in the evaporator there is use of change in temperature. And the gain in heat is used in subsequently in the calculation of the evaporation in the evaporator. This makes the calculation of error ( ) in change in temperature  to be important Assuming =  the we have  Error in calculation of heat gain Q Error in calculation of heat gain  5.0 Discussion With regard to the relationship between the feed flow rate and economy it was found that there was a linear but inverse relationship between economy and feed flow rate. This means that as the flow rate is increased the amount of vapour generated per unit steam supplied reduces. These shows that increasing the feed rate may increase the amount of product produced from the last effect in the series but this means that the higher the product is generated the less the steam is utilized in terms of its ability to vaporize the feed solution per kg of steam used7. This clearly shows that if the amount of product and the desired level of concentration are to be achieved at the same time then both the feed rate and steam flow rate should be adjusted appropriately. Increasing of feed rate while keeping the steam rate constant may not be the way forward. In the investigation of the relationship between steam flow rate and economy it was found that an increase in the flow rate of steam resulted in an increase in the economy. The curve shape indicated that the rate of increase of economy was high at lower steam flow rate and as the steam flow increased further the rate of increase of economy with steam flow rate declined. This was an indication that increasing the steam flow rate is a sure way of increasing the amount of evaporation that can be achieved for each kg of steam. The flattening of the curve with a further increase in steam supply was a clear an indication that it reaches a point where a further increase in the level of steam flow would not come with any appreciable level of increase in evaporation. At this point the steam could be seen as not being put to optimal use. It should also be noted that increase in steam flow rate resulted to increase in level of evaporation which means more concentrated product is extracted. If a product concentration is not to go beyond a certain level, then the extent to which the flow rate of steam can be increased will be set by the desired concentration of product. In some cases the level of concentration is to be kept lower than a certain value because highly concentrated product may present a challenge when it comes to pumping. Reduction of pressure in the evaporator was found to increase the economy significantly. The increase in economy with reduction in pressure was found to be more sensitive at pressure close to zero pressure but at values close to 1 bar the sensitivity was lower. While the economy is being increased without an extra cost of consuming extra steam, creating of a negative pressure means some power consumption. The reduction in pressure means that evaporation is achieved at much lower temperatures. Creating of negative pressure could used in concentration of products which are sensitive to temperature to avoid these products being denatured. It is also important to note there is a limit to which negative pressure can be created in the evaporator. This is because we need to ensure that there is a pressure gradient in the evaporators otherwise if the pressure in the first evaporator is very lower, forward movement of feed and vapour generated will not be possible. In making the calculation quantities used such as temperatures readings had errors. The errors were propagated in the values which were obtained after the calculation. 5.1 Conclusion From the experiment one of the important observations is that increasing the feed rate will result to under utilization of the steam. In order to increase the product out put or the capacity it is important to increase the feed rate at the same time increase the steam supply into the evaporator. While increasing the steam rate may increase the economy considerably it is important to be aware of the desired concentration of the product as excess steam rate may result into higher than required level of product concentration3. The experiment has established that negative pressure is one way of increasing the economy of an evaporator and also it is away of ensuring that concentration of products which are sensitive to high temperatures is achieved. References 1 Schaschke, C. Dictionary of Chemical Engineering [Online]; Oxford University Press: New York, NY, 2014; pp 60. http://app.knovel.com/hotlink/toc/id:kpDCE00021/dictionary-chemicalengineering/dictionary-chemical-engineering (accessed Feb 19, 2017). 2 United States Department of Energy, Industrial Technologies Program. Improving Pumping System Performance: A Sourcebook for Industry, 2nd ed. [Online]; Golden, CO, 2006; p. 3. https://www1.eere.energy.gov/manufacturing/tech_assistance/pdfs/pump.pdf (accessed Feb 19, 2017). 3Schaschke, C. Dictionary of Chemical Engineering [Online]; Oxford University Press: New York, NY, 2014; pp 60. http://app.knovel.com/hotlink/toc/id:kpDCE00021/dictionary-chemicalengineering/dictionary-chemical-engineering (accessed Feb 20, 2017). 4 ASME Shale Shaker Committee. Drilling Fluids Processing Handbook [Online]; Elsevier: Burlington, MA, 2005; pp 239. http://app.knovel.com/hotlink/toc/id:kpDFPH0003/drillingfluids- processing/drilling-fluids-processing (accessed Feb 19, 2017). 5Allaby, M. A Dictionary of Earth Sciences, 3rd ed. [Online]; Oxford University Press: New York, NY, 2008; pp 61. http://app.knovel.com/hotlink/toc/id:kpDESE000X/dictionary-earthsciences/dictionary-earth-sciences (accessed Feb 20, 2017). 6Boljanovic, V. Applied Mathematical and Physical Formulas, 2nd ed. [Online]; Industrial Press: South Norwalk, CT, 2016; pp 351. http://app.knovel.com/hotlink/toc/id:kpAMPFE001/applied-mathematical/applied-mathematical (accessed Feb 20, 2017). 8Kahn, M. K. Fluid Mechanics and Machinery [Online]; Oxford University Press: New York, NY, 2015; pp 508. http://app.knovel.com/hotlink/toc/id:kpFMM00004/fluid-mechanicsmachinery/fluid-mechanics-machinery (accessed Feb 19, 2017). 9 Information gotten in during the lab at SCOB190 from the pump used. 10 Kahn, M. K. Fluid Mechanics and Machinery [Online]; Oxford University Press: New York, NY, 2015; pp 303. http://app.knovel.com/hotlink/toc/id:kpFMM00004/fluid-mechanicsmachinery/ fluid-mechanics-machinery (accessed Feb 8, 2017). 11Glass Tube Rotameter. http://www.rotameters.co.in/glass-tube-rotameter.html (accessed Feb 8,2017). Do Λo T1 Tf Λ1 DoΛo wf wcp Λ1 D1 Q2 wcp D1Λ1 D2 Econ 0.5 2216 60.9 29.1 2358 1108 6 797.544 2358 0.13 310.456 918.234 310.456 0.54 134.78 0.5 2216 60.9 29.1 2358 1108 6.05 804.1902 2358 0.13 303.8098 918.234 303.8098 0.54 133.63 0.5 2216 60.9 29.1 2358 1108 6.1 810.8364 2358 0.13 297.1636 918.234 297.1636 0.54 132.48 0.5 2216 60.9 29.1 2358 1108 6.15 817.4826 2358 0.12 290.5174 918.234 290.5174 0.53 131.33 0.5 2216 60.9 29.1 2358 1108 6.2 824.1288 2358 0.12 283.8712 918.234 283.8712 0.53 130.18 0.5 2216 60.9 29.1 2358 1108 6.25 830.775 2358 0.12 277.225 918.234 277.225 0.53 129.03 0.5 2216 60.9 29.1 2358 1108 6.3 837.4212 2358 0.11 270.5788 918.234 270.5788 0.52 127.88 0.5 2216 60.9 29.1 2358 1108 6.35 844.0674 2358 0.11 263.9326 918.234 263.9326 0.52 126.73 0.5 2216 60.9 29.1 2358 1108 6.4 850.7136 2358 0.11 257.2864 918.234 257.2864 0.52 125.58 0.5 2216 60.9 29.1 2358 1108 6.45 857.3598 2358 0.11 250.6402 918.234 250.6402 0.52 124.43 0.5 2216 60.9 29.1 2358 1108 6.5 864.006 2358 0.10 243.994 918.234 243.994 0.51 123.27 0.5 2216 60.9 29.1 2358 1108 6.55 870.6522 2358 0.10 237.3478 918.234 237.3478 0.51 122.12 APPENDIX 1: Variation between of feed flow rate and economy APPENDIX 2 Variation of steam flow rate with economy Do Λo T1 Tf Λ1 DoΛo wcp Λ1 D1 Q2 wcp D1Λ1 D2 Econ 0.5 2216 60.9 29.1 2358 1108 815.4887 2358 0.12 292.5113 918.234 292.5113 0.53 131.67 0.55 2216 60.9 29.1 2358 1218.8 815.4887 2358 0.17 403.3113 918.234 403.3113 0.58 137.14 0.6 2216 60.9 29.1 2358 1329.6 815.4887 2358 0.22 514.1113 918.234 514.1113 0.63 141.69 0.65 2216 60.9 29.1 2358 1440.4 815.4887 2358 0.27 624.9113 918.234 624.9113 0.68 145.54 0.7 2216 60.9 29.1 2358 1551.2 815.4887 2358 0.31 735.7113 918.234 735.7113 0.73 148.84 0.75 2216 60.9 29.1 2358 1662 815.4887 2358 0.36 846.5113 918.234 846.5113 0.78 151.71 0.8 2216 60.9 29.1 2358 1772.8 815.4887 2358 0.41 957.3113 918.234 957.3113 0.83 154.21 0.85 2216 60.9 29.1 2358 1883.6 815.4887 2358 0.45 1068.111 918.234 1068.111 0.88 156.42 0.9 2216 60.9 29.1 2358 1994.4 815.4887 2358 0.50 1178.911 918.234 1178.911 0.93 158.38 0.95 2216 60.9 29.1 2358 2105.2 815.4887 2358 0.55 1289.711 918.234 1289.711 0.97 160.14 1 2216 60.9 29.1 2358 2216 815.4887 2358 0.59 1400.511 918.234 1400.511 1.02 161.72 1.05 2216 60.9 29.1 2358 2326.8 815.4887 2358 0.64 1511.311 918.234 1511.311 1.07 163.15 APPENDIX 3: Variation of pressure and economy Do press Λo T1 Tf Λ1 DoΛo wcp Λ1 D1 Q2 wcp D1Λ1 D2 Econ 0.5 0.01 2216 6.99 29.1 2485.21 1108 -566.995 2485.21 0.67 1589.258 918.234 1674.995 1.144408 363.6788 0.5 0.02 2216 17.5 29.1 2460.9 1108 -297.474 2460.9 0.57 1346.705 918.234 1405.474 1.025467 319.3177 0.5 0.03 2216 24.1 29.1 2445.26 1108 -128.222 2445.26 0.51 1192.106 918.234 1236.222 0.950775 291.2666 0.5 0.04 2216 29 29.1 2433.61 1108 -2.56443 2433.61 0.46 1076.06 918.234 1110.564 0.895321 270.3332 0.5 0.05 2216 32.9 29.1 2424.25 1108 97.44834 2424.25 0.42 982.9353 918.234 1010.552 0.851185 253.6073 0.5 0.06 2216 36.2 29.1 2416.4 1108 182.0745 2416.4 0.38 903.5475 918.234 925.9255 0.813839 239.4046 0.5 0.07 2216 39 29.1 2409.6 1108 253.8786 2409.6 0.35 835.831 918.234 854.1214 0.782152 227.3235 0.5 0.08 2216 41.5 29.1 2403.58 1108 317.9893 2403.58 0.33 775.0294 918.234 790.0107 0.753859 216.508 0.5 0.09 2216 43.8 29.1 2398.17 1108 376.9712 2398.17 0.30 718.7839 918.234 731.0288 0.72783 206.5316 0.5 0.1 2216 45.8 29.1 2993.25 1108 428.2598 2993.25 0.23 535.4806 918.234 679.7402 0.705196 186.4574 0.5 0.15 2216 54 29.1 2373.51 1108 638.5431 2373.51 0.20 466.3892 918.234 469.4569 0.612397 162.0374 0.5 0.2 2216 60 29.1 2358.65 1108 792.4089 2358.65 0.13 315.5042 918.234 315.5911 0.544495 135.6593 APPENDIX 4 F1 First effect F2 Second effect F3 Economy Economy =  APPENDIX 5 F4 Error in calculation of change in temperature Error in change in temperature is calculated as In the experiment temperate has been given with a precision of 0.1 and this is taken to be the error in temperature readings. Now applying equation F5 Error in calculation of heat gain Q The error in measurement of mass flow rate is taken as  Substituting for  , and  at m=6.135 F6 Error in calculation of D1 Error in  Therefore error in  This means at  /s Read More

The number of evaporators can be increased up to 7 beyond which it becomes uneconomical2. Depending on the feeding arrangement there can a number of configuration including; forward feed, backward feed, mixed feed and parallel feed. In this case we are dealing with forward deed and it is discussed further under the next. 1.2.1 Forward feed Forward feeding can be thought of as being the typical feeding method as far as multi-effect evaporators are concerned. Under this configuration there is introduction of steam in the first evaporator with the feed being passed from effect to the next parallel to the vapour from preceding effect.

With this type of arrangement there is an increase in concentration as the feed move along the evaporators6. This type of feeding find application in cases where the resulting concentrated product is likely to degenerate when exposed to high level of temperatures. The withdrawal of the product happens in the last evaporator in the series and a pump is needed for pumping the feed to the first effect. A pump is also needed for removal of the concentrated product from the last effect. For movement of the product in the middle effects, a pump may not be necessary bearing in mind that that there is flow from high pressure region to lower pressure region. 1.3 Mass balance calculation First effect = 0 and therefore =0 In this equation  = the total amount of heat transferred in 1st effect  = the rate of steam supplied in 1st effect  =latent heat of steam supplied in 1st effect  =the feed flow rate =specific heat of water  =the feed temperature  =rate of vapour generated in 1st effect = temperature of steam condensing in 1st effect = final temperature of steam in 1st effect = latent heat of steam condensing in 1st effect Second effect  and therefore   = the total amount of heat transferred in 2nd effect  = the rate of steam generated in 1st effect  = latent heat of steam condensing in 1st effect  =the feed flow rate  = temperature of steam condensing in 2nd effect  =rate of vapour generated in 2nd effect = temperature of steam condensing in 1st effect = final temperature of steam in 2nd effect  = latent heat of steam condensing in 2nd effect 1.

4 Performance of evaporators (capacity and economy) Capacity and economy are the two quantities used in measurement of performance in steam heated evaporator. Capacity simply gives the mass in kg of water that is vapourized in one hour. Economy on the other hand gives the mass in kg of the water vapourized as the feed passes through all the effects for each kilogram of steam consumed. In case of a single effect the economy about 0.8 (cannot go beyond 1). In a multi-effect evaporator with n effects the capacity will be n-times the capacity of a single effect evaporator while the economy will be equal to about 0.8n4. It is should be noted however, increasing the number of effects come with an increase in pumps, pipe work and valves which brings about an increase in operating costs and equipment.

Calculation of economy Economy =  Where the variables are as described in the second effect equation 3.0 Methodology 3.1 Apparatus P1-Metering pump in stainless steel AISI 316, 0-18L/hr @ 2 bar P2 Liquid ring vacuum pump TK5 Air-water separator for vacuum pump, stainless steel AISI 304 TK1 Feed tank in borosilicate glass, capacity of 25 litres TK2 Collection tank for the concentrated product in borosilicate glass, capacity 10 litres TK4 Graduated borosilicate glass collection tank for the condensed steam, capacity of 1 litre SC Steam trap in stainless steel AISI 304 E1 Falling-film evaporator, stainless steel AISI 316 execution on the tube side and stainless steel AISI 304 on the shell side, exchange surface of 0.

27m2 E2 Shell-and-tube condenser, stainless steel AISI 316 on the tube side and stainless steel AISI 304 on the shell side, exchange surface of 1.1m2 E3 Tube-tube heat exchanger in stainless steel AISI 304 PI1,PI2 2 Bourdon pressure gages, range 0,6 bar PI3 Bourdon pressure gage, range of 0, 1.

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