CHAPTER V TOE COMBUSTION EFFICIENCY OF DIFFERENT BOILER SYSTEMS* EXPERIMENTAL OESUX.TS Chapter Preview

Transcription

1 CHAPTER V TOE COMBUSTION EFFICIENCY OF DIFFERENT BOILER SYSTEMS* EXPERIMENTAL OESUX.TS Chapter Preview This chapter attempt to analyse the combustion efficiency of different boiler systems like lancashire, package and fluidised bed combustion (FBC) boilers when coal and lignite are (combusted) used as fuel input. It provide the results of combustion efficiency analysis, especially the optimum efficiency parameters and identify " the least cost steam generation scenario of each boiler technology group separately for coal and lignite consumption process. This chapter also explain the pollution emission intensity of lancashire, package and FBC boilers when coal and lignite are combusted (also the pollution emission and efficiency relationships). The last part of this chapter enlist the results evolved from the analysis Introduction With a view to understand the extent of combustion efficiency variation between different boiler technologies, and as a basic experimental supporting evidence for the economic and the energy policy implications (and environmental implications) of the boiler replacement efforts an attempt is made here to gather experimental evidence regarding the energy efficiency through the combustion efficiency investigation of different boiler systems. An effort is also made to understand the combustion efficiency/inefficiency and the respective pollution emission relationships. Twentyfour experimental results were gathered from the integrated and detailed energy audit conducted among various units where Lancashire, Package and Fluedised Bed Combustion (FBC) boilers of different types are functioning. For the sake of fuel homogenity the data regarding coal and lignite only were considered for analysis. Though data on natural gas and oil was available for a few energy audits, only lignite and coal were considered for the analysis here (due to lack of fuel homogenity among all the different 150

2 boiler groups). When Package boiler and FBC boilers are able to accept different types of fuels like coal^ lignite, agrowaste and oil, the lancashire boiler technology usually could combust only lignite and coal. Because of this fuel acceptancy limitation among the different boiler groups chosen for the analysis, the flue gas analyser based data for coal and lignite from lancashire, package and FBC boiler are taken up for combustion efficiency analysis Combustion Efficiency Variation Among Different Boiler Groups Though many factors like air fuel ratio, air preheating, waterpreheating, steam distribution system etc, play a significnat role in determining the final effective energy efficiency in all types of boiler steam using systems, the ultimate single factor which helps enhance energy efficiency is the boiler technology. Twenty four experimental case study data are analysed to identify the energy efficiency variation among lancashire, package and FBC boilers of different types. All these combustion efficiency investigations are carried out using a sophisticated flue gas analyser which can monitor information on carbon-monoxide (CO,), carbon dioxide (CO,), sulphur dioxide (SO,), nitrogen dioxide (NO,) and suspended particulated matter (SPM). (The conventional flue gas analyser is able to investigate only three parameters like CO, CO, and temperature. But the one used (during the Energy Audit) to obtain the data for the analysis here is having both energy efficiency indicators and pollution indicators). Because of operational constraints the homogenity of design capacity of the boilers on which the flue gas analysis was conducted could be maintained. Further, the experimental data on the same boiler for f the different fuels were not available (i.e. the flue gas analysis experiment in the same boiler in which different fuels were used were not available). Hence, four observations each for the same type of boiler was taken for coal and lignite only. Also the design capacity of the boilers chosen were different. Therefore, the twenty four case studies are independent by itself. However, the design capacity and fuel heterogeneity will not affect the basic objective of this analysis, i.e,, finding out the combustion efficiency of different boiler systems and propensity (intensity) of pollution emission. 151

3 Flue gas analysis data for eight lancashire boilers, eight package boiler and eight FBC boilers were collected from the energy audit (reports/documents) case studies. Though, all these twenty four cases happened to be of different fuel mix and different capacity mix, it is conceptually possible to arrive at a systematic comparative observation among different boiler technology mix and fuel mix, The Cumbustion Efficiency of Lancashire Boiler: Lancashire boiler is the major boiler system operating in Ahmedabad. As discussed in Chapter VII out of the total 1349 boilers, 752 boilers (together accounting for a total capacity of 3604 ton, i.e., 53.13%) are belonging to lancashire variety. These are of different capacity types ranging from 0.5 ton to more than 15 ton. However, in the flue-gas analyser based experiment, data on boilers ranging between 1.5 ton to 5 ton only could be identified. Out of this, two 2 ton boilers, one 4 ton boiler and one 1.5 ton boilers were taken for coal combustion efficiency analysis. Another four boilers of 2, 3, 4 and 5 ton capacities were taken for lignite combustion efficiency analysis (of lancashire technology). It would have been more compatible conceptually if the data of the same boiler in which both coal and lignite were burned (at different times) was undertaken for a flue gas analysis experiment. But practically that was not possible as running fuel could not be replaced during the energy audit. A minor conceptual difficulty is - that when one type of design capacity is observed in the flue gas analysis experiment of coal, another type of capacity is observed in lignite combustion efficiency experiment. Once again, this difficulty is due to the independent nature of energy audit conducted for different boilers at different time periods, in which no comparative analytical consideration was given to the design capacity concept of a particular boiler technology system when the flue gas analysis experiment for the energy audit is made. The ultimate energy efficiency (hence the energy economy) is basically depending upon the fuel mix and the boiler technology. Considering this critical criterion, the flue gas analyser data for both coal and lignite for lancashire boiler technology was gathered and analysed to understand the combustion efficiency variation in the 152

4 same type of boiler when two different fuels are used. In the present experimental investigation encompassing eight boiler systems, a systematic parameter profile was adopted. Table 5.1 shows the different technical profiles of the boiler like, design capacity and operating capacity, combustion profile like fuel consumed and specific fuel consumed, steam cost based on fuel consumption, air fuel ratio. The determinents like the percentages of CO and CO,, temperature, etc. were considered for determining the combustion efficiency. Using all these parameters, combustion efficiency could be determined with a greater degree of preciseness, The Combustion Efficiency of Coal fed Lancashire Boiler Out of the four observations the maximum efficiency was observed in case of A, which is a boiler having 2 ton design capacity and 1.60 ton operating capacity. The lowest efficiency was observed in case of D,, which is having 1.5 ton design capacity and 1.20 ton operating capacity. The specific fuel consumption parameter and CO, percentage are the basic indicators of combustion efficiency. Interestingly in the case of A, which is having the maximum efficiency (59.10%) the specific fuel consumption for generating 1 ton of steam is having the lowest coal consumption of 237 kg/hour. Correspondingly, in case of CO,, it is having the maximum percentage point of 6.10% and minimum of CO, (250 ppm) subsequently indicating the maximum efficiency. The cost of 1 ton of steam production is also lowest in this case where it is Rs In the case of D, which is having the lowest combustion efficiency (49.20%) the specific fuel consumption is maximum (285 kg/hr.) and the cost of 1 ton of steam production is Rs The CO and CO, emission of this boiler is also consistent with high CO emission of 320 ppm and low CO, emission of 5.23%, characteristic of inefficient burning process. The average combustion efficiency of all the four observations of lancashire boiler using coal as the fuel input is 54.51%, though the highest efficiency is 59.10% and lowest efficiency is 49.20%. This variation of 9.90 percentage points between the highest and lowest efficiency may be attributed to the difference in the calorific value and ash content of fuel, status of burner, and other operating factors. 153

5 5.1.4 The Combustion Efficiency of Lignite fed lancashire Boiler Four cases are taken for experimentally investigating the combustion efficiency of lignited-fed lancashire boiler. The design capacity of these boilers are of 2 ton, 3 ton, 4 ton and 5 ton. Out of the four, D, is having the maximum combustion efficiency of 55% and C, shows the lowest efficiency value of 47.20%. In both the cases the energy efficiency indicators are consistent. When the major energy efficiency indicating factor, i.e., cost of production of 1 ton of steam is lowest (Rs ) in case of D,, C2 which is having the lowest efficiency, shows the highest cost of steam generation (Rs ) among the four boilers selected for the efficiency investigation. A comparative analysis of all the four obsevations in the coallancashire combination and the four lignite- lancashire combination shows a perfect consistency in case of the major combustion efficiency determinants like specific fuel consumption, cost of production of steam generated, CO and C02 emission factors, (Table 5.1). The important observation emerging out of this analysis is that the lancashire-lignite combination is having the maximum energy economy, as the lowest cost of production per ton of steam generation is realised in this boiler fuel combination group. Though the general combustion efficiency is lower in case of lancashire-lignite combination compared to lancashire-coal combination, the maximum energy economy is observed in case of lancashire- lignite group. Another important fact emerging out of this analysis is that combustion efficiency is not exactly consistent with the economy of steam generation. However it may be mentioned that the combustion efficiency variation found among the lancashire-coal and lancashire-lignite combination is due to the calorific value variation between coal and lignite, (the boiler - technology remaining constant) and the energy economy variation is due to the variation between coal price and lignite price. Thus, it could be substantiated from the above experimental results that the ultimate energy economy is depending upon the technological factors governing the boiler, the physico-chemical factors governing the calorific value of different fuels and the economic factors governing the price of energy input like coal, lignite, etc Combustion Efficiency of Package Boilers Package boiler (of different types) is one among the major technologically efficient boiler systems which gives a very high energy efficiency compared to the conventional lancashire boilers. Though this is an accepted fact, borne out by experience, studies establishing the specific efficiency with regard to different fuel mix and design capacity mix are not found frequently among the technical literature and research reports dealing with energy conservation. Therefore, to establish experimentally the efficiency profile of package boilers, flue gas analyser data is analysed as done in the case of lancashire technology. Eight cases were analysed 154

6 to find out the combustion efficiency of package boilers using coal and lignite. Though package boilers are also using oil and natural gas, those observations were not considered for analysis here, since the result of this has to be compared with the result of lancashire boiler, which use usually Only coal and lignite Combustion Efficiency of Coal fed Package Boiler Data pertaining to Four boilers having different design capacities varying from 2 to 8 ton are analysed. Out of the four boilers one was that of 2 ton, the second one was that of 3 ton type and the third and fourth were that of 4 and 8 ton design capacities. Among the four coal using package boilers the one having the higher capacity of 8 ton (D,) showed the maximum combustion efficiency of 75.51%, Consistent with the general efficiency characteristics, this particular boiler showed the minimum specific fuel consumption per ton of steam generated and also lowest stream cost. The 2 ton capacity package boiler showed the lowest combustion efficiency of 72.10%, 3 ton capacity boiler registering a 72.34% and the 5 ton showing a 73.40% (Table 5.2). In all these cases there is a consistent manifestation of combustion efficiency determinants. C,, which is a 2 ton type happened to be the least efficient one, which registered a highest cost of steam production of Rs per ton, when the highest efficiency boiler Dj registered the lowest cost of steam production of Rs per ton of steam generated. Also when the combustion efficiency parameter like CO, is considered, D, is having the maximum CO, of 10,10% indicating the highest efficiency among all the four. In the case of C,, which is having the lowest combustion efficiency, CO, is also having lowest value of 8%. The excess air parameters also showed the same sequential tendency when D, is having the excess air percentage of 74.51, the least efficient boiler C,, showed an excess air percentage of , confirming the consistency among the combustion efficiency determinents. When the average efficiency of all the four boilers is 73,34%, the lowest efficiency is 72.1% and the highest efficiency is 75.51%, thereby showing a small difference between the highest and lowest efficiency values, unlike in the case of laneashire-eoal combination. One major observation emerging from this analysis is that the high capacity boiler is having morn Combustion efficiency and the low capacity boiler is having less 155

7 efficiency. However, the impact of the other boiler efficiency determinants explained earlier should also be considered before identifying one major single determinant. Thus, it is clearly evident that the combustion efficiency determinents are more or less having similar characteristic functioning pattern both in case of lancashire-coal and package-coal combinations. 5.1,8 Combustion Efficiency of Lignite-fed Package boiers Four boilers having design capacity ranging between 2 ton and 6 ton, were selected for the combustion efficiency analysis among package boilers. Here also one boiler was 2 ton, the second one was 3 ton and the others were that of 5 and 6 tons of design capacity. The average combustion efficiency is 67.53%, which is approximately 6 percentage points less efficient than the coal-fed package boilers. As observed in tha case of package-coal combination, here also the higher capacity boiler registered the maximum efficiency (69.80%) and the smaller capacity boiler shows the lowest efficiency (65,20%). The combustion efficiency determinents like CO and CO, also showed a consistent behaviour influencing the final combustion efficiency. When the C, boiler which registered the highest combustion efficiency is having the highest CO, emission the lowest efficiency boiler, D,, indicate a lowest CO, of 2.4%. The same efficiency trend is observed in case of CO emission where the lowest efficiency boiler showed the highest value of 220ppm and the highest efficiency boiler showed the lowest CO emission (150 ppm), correspondingly the specific fuel consumption values also show a consistency. The specific fuel consumption for the highest efficiency boiler (C,) is 238 kg/hour and for the lowest efficiency boiler it is 254 kg/ton of steam generated. The steam cost parameter also was consistent. In the case of the high efficiency boiler it was Rs and in case of the lowest combustion efficiency boiler, it was Rs, Thus, a perfect consistency among all the boiler efficiency determinents are observed including the excess air factor (Table 5.2.). From the above experimental results obtained for the four coal- fed package boilers and four lignite-fed package boilers, it could be concluded that the combustion efficiency determinant behaved in a set pattern in all the cases and the highest capacity boiler shows 156

8 highest efficiency and lowest capacity boilers show the lowest efficiency both in case of coal consuming and lignite consuming boilers. When such a consistent observation is emerging from the analysis of the package boilers, the same pattern is not exactly emerging from the lancashire boilers. In case of lancashire boilers this consistency was not observed among the coal-lancashire combination, but among the lignite consuming lancashire boilers this consistency is clearly emerging. Hence, it could be concluded that in all the cases the combustion efficiency parameters behaved in an exactly set pattern and in majority of cases the high capacity boilers registered a high efficiency and the low capacity boilers showed a low efficiency pattern Energy Efficiency of Fluedised Bed Combustion (FBC) Boilers FBC boiler is the most efficient boiler existing at present. Not only FBC boilers are efficient but also this is the only boiler technology which can accept almost all types of solid, liquid and gaseous fuel resources. FBC boiler also emit less pollution compared to other alternative boiler technologies. (As in the case of package boilers, flue gas analyser based combustion efficiency data for FBC boilers are also found less). Hence, the combustion efficiency experiment for FBC,boiler is very useful and essential for establishing experimentally the combustion efficiency intensity and the factors which determine the combustion efficiency Combustion Efficiency of FBC boilers using Coal To experimentally establish the combustion efficiency of FBC boilers, eight boiler systems having different capacities and seperate fuel and boiler mix were selected. When data for low capacity lancashire and package boilers are available, in the case of FBC boilers such data are not available. Hence, the boiler capacity chosen for FBC analysis is between 5 and 12 tons. Out of the eight boiler systems, four systems were using coal and the other four lignite. The average combustion efficiency observed among the coal consuming FBC boiler is 79.79%. Four boilers using coal were selected for the flue' gas analysis experiment to establish the combustion efficency. Out of the four systems, two boilers were of 8 ton capacity, one boiler of 12 ton capacity and the other one is 157

9 coining in the category of 6 ton capacity. Interstingly, the efficiency among the four boilers varied between 77.92% to 81.12%. Theoretically, it is most encouraging that the 12 ton capacity boiler registered the maximum combustion efficiency of 81.12%. However, the 6 ton capacity boiler showed more efficiency (79.60%) than that of the 8 ton boiler system (A,), which is slightly contradicting the earlier established combustion efficiency characteristic pattern observed in case of package and lancashire boilers. Yet, one 8 ton capacity boiler (C,) showed the second highest efficiency of 80.50%, when the other 8 ton boiler showed the lowest combustion efficiency of 76.38%. This minor discrepency is caused, may be, due to non- technological parameters. However, the energy efficiency parameters like, specific fuel combustion and steam cost per ton of steam generated are fully consistent with other observations. The steam cost per ton of steam generated is least in the case of the unit B, (Rs ) which is having the maximum combustion efficiency of 81.12%. This combustion characteristics is consistently observed in all the four cases. Also other efficiency determinants like CO, CO, contents and excess air supply also show a clear consistency. For example, unit B, which is having a combustion efficiency of 81.12% is also having the lowest CO value and highest CO, value, thereby indicating that irrespective of the boiler technology type the efficiency determinants decide the ultimate efficiency, the fuel remaining constant. It may be argued that the efficiency determinants are directly influenced by the technology factors. However, the general combustion efficiency characteristics observed among the other boiler types which are using coal is also observed in case of coal consuming FBC boilers. When more efficiency variation was observed among the same type of boiler using the same type of fuel mix, in the case of FBC boilers, the efficiency variation observed is having very low range 9Table 5.3) The Combustion Efficiency of Lignite using FBC Boilers FBC boiler, as explained earlier, is a versatile boiler technology which can accept an array of different fuels having different effective thermal efficiency pattern. To understand the combustion efficiency characteristics of lignite using boilers, four units having capacity ranging from 5 to 10 tons were selected, viz. 5,6,8 158

10 and 10 ton design capacities. Here, somehow, the lower capacity boiler system showed a high combustion efficiency of 76.60%. The ^ high design capacity.boiler somehow showed 76.38% combustion efficiency compared to the 78.60% of combustion efficiency shown by the low capacity boiler* of 8 ton. When the average combustion efficiency of lignite using PBC is 76.85% the highest efficiency is 76.60%. The largest capacity boiler showed almost the same value of the average capacity (76.35%), Here also the energy efficiency factors maintained consistency. The specific fuel consumption and the steam cost factors were more in the case of maximum efficiency boiler system and minimum in case of less efficient units. The excess air factor also maintained consistency. Another major observation evolving out of the analysis of these four boiler systems is that lignite using PBC is having the lowest cost for producing one ton of steam. At the same time, among the coal using FBC boilers and coal and lignite using package boilers, the coal using FBC system shows the least cost, i.e., Rs.129,77 per ton of steam generated. Thus, the most efficient and economic boiler-fuel combination is FBC- lignite combination, especially when the most important parameter, i.e., the cost of generating one ton of steam, is considered. When this particular factor is compared with the other boiler fuel combination systems the difference is very significant. For example, in the lancashire-lignite combination, the maximum cost for generating one ton of steam is Rs , among package-lignite combination it is Rs.156,21 and in FBC-lignite combination it is Rs , Therefore, if one considers the cost between lancashire and FBC, it is 38.07% higher in the case of lancashire boiler system (Table 5.3) Fuel Mix and Combustion Efficiency of Different Boilers Though each boiler technology, like lancashire, package and FBC has got its own efficiency endowments, the ultimate efficiency of a particular boiler system is realised when the optimum boiler technology combination, and fuel mix combination is achieved. As discussed in the earlier part of this chapter each fuel is having its own characteristic efficiency attributed to its physico-chemical nature (carbon content). Hence analysis of each boiler type and its fuel mix results the has to be examined. 159

11 5.2.1 Fuel mix and Combustion Efficiency Relationship among the Lancashire Boilers Lancashire boiler technology is such that it can usually accept only lignite and coal, though agrowaste can also be accepted with some technological modifications. For the analysis here four lancashire boilers using coal and other four lancashire boilers using lignite are chosen for the fuel mix technology analysis. Table 5.1 presents a comprehensive picture of fuel mix and boiler technology mix. Among the lancashire boilers the maximum economy in steam cost is realised in case of observation A, having 2 ton capacity and coal as basic fuel. In this case Rs was the cost of 1 ton of steam generated, when observation showed a steam cost component of Rs which is 16.84% more than the maximum combustion efficiency observation. When lignite is considered for inter unit efficiency variation'and steam cost comparison, the difference is 14.20% between the highest and the lowest efficiency values (Table 5.1), This shows that the efficiency variation between the different fuel combination of coal and lignite is not having much difference. However, the design capacity, the operating capacity and the fuel type is having an inherent relationship. In the case of coal, the 2 ton capacity boiler showed more combustion efficiency than the 4 ton capacity boiler. However, this pattern of relationship is not observed in case of lignite using lancashire boilers. In the lancashire-lignite combination the maximum capacity boiler recorded the maximum efficiency, logically leading towards a conclusion that high design capacity and lignite fuel mix gives more steam economy and combustion efficiency (Table5*l). The same characteristic pattern between the fuel mix and design capacity is not observed in case of lancashire-coal combination. Though the number of observations are inadequate to apply the standard statistical techniques, it can be concluded that fuel mix and design capacity of the boiler have some relationship. It is interesting that when the design capacity and fuel mix relationship is analysed, the package and lancashire boiler show a similar pattern, i.e., the high capacity boiler in both the cases, (when lignite is used) gives maximum combustion efficiency and minimum steam cost. However, this particular trend is not exactly emerging 160

12 in case of FBC-lignite combination, where the 8 ton capacity boiler showed more steam economy and maximum combustion efficiency, than the 12 ton capacity boilers. Thus, when there is a similarity between package and lancashire boilers, the same similarity is not observed in case of FBC boilers. Under these circumstances it may be concluded that boiler technology remaining constant, the fuel mix and design capacity are the major parameters attributed to general steam economy Fuel mix and Combustion Efficiency Relationship among Package Boilers * Out of the eight case studies taken for the package boiler group, four were coal consuming and the other four lignite consuming. Among the coal consuming case studies D! which is having an 8 ton capacity boiler registered the maximum combustion efficiency and minimum steam cost. Interestingly, there is a unique pattern among the four case studies. As the design capacity increased there is a direct progressive relationship and combustion efficiency, i.e, in all capacity increased, the steam cost efficiency increased among the coal 5.2). from 2 to 8 tons between design capacity the four cases, as the decreased and the combustion using package boilers (Table The lignite using Package boilers also showed that the maximum capacity boiler achieved the maximum efficiency and the minimum steam cost. In this subset of Package boilers also, an exactly uniform pattern of efficieny and fuel economy evolved. When the design capacity of the boiler increases the combustion efficiency also increases and the steam cost decreases in a orderly fashion. Thus, both package-coal combination and package-lignite combination proves that high capacity boilers, irrespective of fuel mix, gives an orderly pattern of increased combustion efficiency and subsequent steam economy benefit Fuel mix and Combustion Efficiency Relationship Among FBC Boilers Though the maximum capacity boiler emerged as the maximum effficient fuel combustion system, the progressive trend between the design capacity and fuel mix is not exactly emerging among the FBC boilers 161

13 as observed in the case of lancashire and package boilers. It can be seen from Table 1 that D, which is having the lowest design capacity is having more fuel economy and combustion efficiency than the unit A,, where an 8 ton FBC boiler is in operation. This trend, to a greater extend, is contradictory to the pattern evolved in cases of package and lancashire boilers. When one come to the iner-unit variation, the steam cost and combustion efficiency difference is not very wide as observed in case of lancashire and package boilers. The results of the four boiler systems using coal clearly indicate that among the FBC boilers, the inter-unit variation of steam cost is not much pronounced. Yet, in case of combustion efficiency, it varied between 81.12% to 71.72%. Similar trend is also observed among the FBC lignite combination group, where the efficiency varied between 78.60% and 76% (Table 5.3). Here, though the 10 ton boiler is having the largest capacity, its fuel economy and combustion efficiency were lower than 8 ton boiler of C, unt. This observation leads to the conclusion that the design capacity and fuel mix is not having a positive relationship among the FBC boilers. Ultimately when the comparative analysis of all the three boiler systems along with their respective steam cost economy and combustion efficiency are compared, there is a positive and orderly relationship between the design capacity, fuel mix, steam cost economy and combustion efficiency among the lancashire and package boilers and such a relationship is not strictly observed among the FBC boilers. Yet, from the majority observations it can be concluded that higher the boiler capacity, more the steam economy and combustion efficiency Environmental Implications of Different Boilers The boiler technology not only determines the combustion efficiency, but also the different pollution emission. In fact, there is a direct relationship between the efficiency of a boiler and the pollution emission, that is, more the boiler's efficiency, less the pollution emission. However it is most interesting that when the boiler efficiency increases, the sulphur dioxide (SOj), Nitrogen dioxide (NOj) and suspended particulate matter (SPM) decreases. When SPM, NOj and S0! emission decreases, in case of C02 the emission increases. In other words, an increase in boiler efficiency results 162

14 into a corresponding increase in CO, emission. The results of the analysis of these relationships (the pollution emission characteristics of three different boiler systems) are now presented, Efficiency and pollution emission relationship observed among the Lancashire Boilers The efficiency analysis shows that lancashire boiler is the most inefficient one compared to package and FBC boilers. Eight different energy audit case studies taken for efficiency analysis are considered for the pollution emission analysis also. In all these cases four different pollution parameters are considered. They are SO,, NO,, SPM and CO,.Table 1 explains the different efficiency and pollution details of lancashire boilers. Four cases using coal and another four cases where lignite is used as the input are taken for the comparative analysis (Table 5.1). Among the coat using group two boilers are of 2 tonne capacity, one is of 4 tonne capacity and the fourth one is of 1.5 ton capacity. When the SO, emission is considered, almost all the four cases give the same emission rate, with one exception. The units A, and B, each of which are having 2 tone design capacity showed respectively 7.11 kg/ton and 7.68 kg ton steam generated. The 4 ton boiler using unit showed 7.62 kg/ton of steam generated. However the unit D, which is having 1.5 ton design capacity showed an increased SO, emission of 8.55 kg/t of steam generated. This shows that as the efficiency decreases the pollution emission rate increases. In case of NO, also the lowest efficiency boiler (D,) showed the highest emission value of 2,85 kg/ton of steam generated. The maximum design capacity unit showed NO, as 2.5kg/ton of steam generated. The 2 ton capacity boilers showed 2.56 and 2.37 kg of NO, per ton of steam generated. The SPM emission also shows that the lowest efficiency boiler is having the maximum emission (5.70 kg/ton of steam). The boiler having maximum efficiency showed the minimum emission rate of 5.08 kg/ton of steam generated. In the other two cases where the efficiency is more or less same, the emission rate is 5.12 and 4.74 kg/ton of steam generated. The CO, ' emission characteristics give an altogether different picture. The most efficient unit emits the maximum CO, pollution. 163

15 Among the four coal using lancashire systems, unit A, is having 59.10% of efficiency and the same unit is having the maximum CO, emission also (66 kg/ton of steam generated). The unit D, is having the lowest efficiency of 49.20% and also the lowest pollution emission of kg/ton of steam generated. The same type of relationship is observed in case of B, and C, unit, between the efficiency parameter and CO, emission. It is interesting to observe that when the lowest efficiency boiler produces more SO,, NO,, and SPM pollution emission, in case of CO, it is the lowest. Thus, it is emerging that the pollution emission intensity and the boiler efficiency is related both negatively and positively in case of coal using lancashire boilers. To understand the boiler efficiency and pollution emission relationship among the lingnite using lancashire boilers four cases were taken up for detailed analysis, Unit A, having 4 ton, B, - 3 ton, C, - 2 ton and D, - 5 ton were taken for the lignite category. Almost all the pollutants except CO, are having double the amount of pollution compared t;o the coal using lancashire boilers. The SO, emission observed in the lignite category is varying between and kg/ton of steam generated. In this category the maximum boiler efficiency (55%) unit is having the minimum emission of kg/ton of steam generated. The unit C, which is having the lowest efficiency of 47.20% is having the highest SO, emission of kg/ton of steam generated. Unit A, which is having 53.20% efficiency showed an SO, emission of kg/ton of steam generated and unit D, having the efficiency of 51.50% showed an emission rate of 4.83 kg/ton of steam generated. All these four observations show that less the boiler efficiency, more the SO, emission. The NO, emission is also almost double in case of the lignite using boilers compared to the coal using lancashire units. Among 4 units, unit D, having the maximum efficiency recorded the minimum pollution emission and the lowest efficiency unit recorded the maximum NO, emission of 5.28 kg/ton of steam generated, thereby indicating the consistency observed in case of SO, emission. The SPM also shows the same type of trend observed in case of SO, and NO,. Here also the emission is almost double compared to the coal using lancashire boilers. Again the lowest efficiency boiler (47.20%) showed the highest SPM emission of kg/ton of steam generated. The 164

16 maximum efficient unit (55%) showed the lowest SPM emission of 9.06 kg/ton of steam generated. The unit A, which is having an efficiency of 53.20%, recorded an SPM emission as 9.66 kg/ton of steam generated. Thus, in case of SPM also it is clearly emerging that the high boiler efficiency result into lowest SPM emission and vice-versa (Table 5.1). It is observed that the lignite using boilers are having comparatively less CO, emission than the coal using ones. (It may be mentioned that this difference is attributed to the carbon content variation between coal and lignite. As coal is having more carbon content compared to lignite, it leads to more thermal efficiency and hence more COj emission). The energy efficiency and CO, emission characteristics relationship observed in case of coal is also consistently emerging in case of lignite using lancashire boilers also. The unit D, is having maximum efficiency of 55% and also having the maximum CO, emission of 58,40 kg/ton of steam generated. The unit C, which is having the lowest efficiency recorded the lowest CO, emission of 51.50%. This is again consistent with the efficiency and CO, emission relationship observed in case of coal using lancashire boilers. The other two units also show the conisistent relationship, i.e., highest efficiency and highest CO, emission. The above analysis leads to the following observations. The boiler efficiency remaining constant the pollution emission will vary depending upon the fjuel used. Here, the coal using lancashire boilers recorded less pollution emission in case of SO,, NO,, and SPM compared to lignite using lancashire boilers, where the pollution emission is almost double. The other major observation emerging out of this analysis is, as the boiler efficiency increases, the SO, emission also correspondingly increases. However, the efficiency is more with coal using lancashire boilers and these units also emitted more CO, compared to the lignite using lancashire boilers which are having less efficiency, and less CO, emission. Therefore, it is apparent that more the boiler efficiency, less the pollution emission of SO,, NO, and SPM and more the emission of CO, (Table 5.1). 165

17 5.3.3 Efficiency and Pollution Emission Relationship Observed Among the Package Boilers As in the case of lancashire boilers, 8 cases of package boilers using coal and lignite are analysed for understanding efficiency and pollution emission relationships. Four boilers using coal and other four boilers using lignite is taken up for the analysis. All the above 8 boilers are having different design capacities varying from 2 to 8 tons (Table 5.2). Among the coal using package boilers one unit is that of 2 ton capacity, another one 3 ton, and the remaining two 5 and 8 ton capacities. The unit D, is having an 8 ton capacity boiler and the same is observed as having maximum efficiency of 75.51%. Correspondingly, the pollution emission of SO,, NO, and SPM are the lowest and CO, is the maximum. The SO, value observed is 5.58 kg/ton of steam generated, NO, is 1.8 kg/ton of steam generated, SPM 3.72 kg/ton of steam and CO, kg/ton of steam. The lowest efficiency (72.10%) is observed in case of C, unit which is having a 2 ton capacity boiler. The pollution emission is also high especially in case of SO, (5.82 kg per ton of steam generated) (kpts), NO, (1.94 kpts), SPM (3.88 kpts) and lowest in case of CO, (76.30 kpts). These observations between C, and D, shows that the design capacity and the boiler efficiency is related; in the sense that, high design capacity shows high efficiency and vice-versa. Another apparent characteristics emerging is that more the efficiency less the pollution of SO,, NO, and SPM and, more the efficiency, more the CO, emission. In short, more the design capacity, more the efficiency, and more the efficiency less pollution of SO,, NO, and SPM and more pollution of CO,. This observation is also consistent with the result of the other two units (A, and B,) using 3 and 5 ton capacity boilers. The 3 ton capacity boiler shows an efficiency of 72.34% and 5 ton capacity boiler registered 73.40% efficiency. The pollution emission characteristics are also consistent in these two cases. Thus, these four observations of coal using package boilers, in general, show a consistent pattern with the coal using lancashire boiler. That is more capacity boiler shows more efficiency, and more efficient-boiler emit less pollution in case of SO,, NO, and SPM and more pollution in case of CO, (Table 5.2). 166

18 The 4 lignite using package boilers taken up for the analysis are having different capacities ranging from 2 to 5 ton. Unit D, is having 2 ton capacity boiler, unit B,-3ton unit A,-5 ton and unit C,-4 ton. As in the case of coal using package boiler, here also the high capacity boiler is having more efficiency and less S02, NO, and SPM pollution emission. Unit D2 which is of 2 ton capacity recorded less pollution and showing an efficiency of 72.10% and S02, NO, and SPM emission as kptsg, 3.82 kptsg and 7.62 kptsg. The CO, emission is the lowest having kptsg. The highest efficiency (69.80%) is observed in case of unit C, having a 6 ton boiler. The lowest emission rate is also observed in this case as far as SO,, NO, and SPM is concerned and highest emission of CO,. The other two units also reveal the same characteristic trend as far as efficiency and pollution emission relationship is concerned. As observed in case of lancashire boiler, the coal using units are having more efficiency and lignite using units are having less efficiency in case of package boilers also. The pollution emission characteristics are also same among package and lancashire boilers, i.e., lignite using units emit almost double the quantity of SO,, NO, and SPM pollution compared to coal using ones. Thus, it is becoming evident that among both lancashire boiler and package boiler (using coal and lignite), the efficiency characteristics and pollution emission characteristics are having a similar trend. When compared between fuels, the lignite using units are less efficient and coal using units more efficient. In case of pollution emission, lignite using units emit more pollution and coal, using units emit less SO,, NO, and SPM and more CO, pollution (Table 5.2) Efficiency and pollution emission relationship observed among the FBC Boilers Eight units are chosen for understanding the efficiency and pollution emission relationship prevailing among the FBC boilers. Out of the eight units, four units use coal and other four units use lignite. The boiler design capacity is heterogenious in all the eight cases. When low capacity boilers are more frequent among the package and lancashire boilers, the lowest capacity among the FBC boiler group is that of 5 ton. boilers are found among the FBC group. boiler found More high capacity 167

19 To identify the boiler efficiency and pollution emission relationship among the coal using FBC boilers four units are selected. Two units are having 8 ton capacity each, one unit 12 ton capacity and the fourth one having 6 ton capacity (Table 5.3). As observed in the package and lancashire boiler group, here also the maximum efficiency is recorded with the largest capacity boiler (12 ton). The emission rate of SO,, NO, and SPM are also lowest and the CO, is highest among all. The maximum efficient unit (B,) is having the highest capacity boiler (12 ton). It recorded 81.12% of efficiency which is highest among all. The pollution emission of SO,, NO, and SPM are also lowest among all and that of CO, is highest. The corresponding values of different pollutants are SO, 4.59 kpts, NO, 1.33 kpts. and SPM 3.5 kpts and CO, kpts. The lowest capacity boiler recorded an efficiency of 79.60% which is the lowest among the coal using FBC boilers group. The pollution values are correspondingly the highest. They are SO, 4.68 kpts, NO, 1.36 kpts and SPM 3.10 kpts. The CO, value is, however, not lowest. It is puzzling that unit A, and B, which are having 8 ton capacity boilers show different efficiency. Unit A, shows 77.92% efficiency and unit C, is having 80.50%, This observation is inconsistent with the trend observed among the other boiler groups. It is also observed among this group that unit A, having an 8 ton boiler registered 77.92% efficiency which is the lowest, and unit C, having the same 8 ton capacity boiler showed 80.50% of efficiency. These two observations are rather inconsistent with the trend observed among the other boiler groups. Unit D, having the lowest design capacity registered more efficiency (79.60%), and unit A, having 8 ton capacity registered 77.92% efficiency, thereby, indicating a contradictory design capacity and efficiency relationship characteristics. However, the efficiency and pollution relationship characteristics observed among the other boiler groups are consistent among this group also. The unit B, using a 12 ton boiler is having the highest efficiency of 81.12% and the lowest emission of SO, (4.59 kg/t), NO, (1.33 kg/t) and SPM (3.05 kg/t). This unit registered a maximum emission of CO, (81.72 kg/t). The unit A, having an 8 ton boiler recorded the lowest efficiency of 77.92% and highest emission rate of SO, (4.80 kg/t), NO, (1.40 kg/t) and SPM (3.15 kg/t). The CO, emission was lowest in this case having kg/t. Though there exists a difference between the design capacity and efficiency, the consistency between efficiency and pollution emission is observed in 168

20 this case also. Therefore, what is emerging is that among the different type of boilers like lancashire, package and FBC, using coal as an energy input, more the efficiency less the emission of 50., NO, and SPM and more the CO, emission (Table 5.3). To understand the efficiency and pollution emission relatinship among the lignite using FBC boilers, 4 cases were selected. The design capacity- of these four units varied between 5 ton and 10 ton. Among the four units, unit A, having 10 Ton capacity registered 76.38% of efficiency ' (which is inconsistent with the earlier observations). However, unit C, having an 8 ton boiler recorded more efficiency (78.60%) compared to unit A,. Also in case of pollution emission, unit A, shows an inconsistent characteristic compared to other units which show a decreasing trend in pollution emission of 50., NO, and SPM with increasing efficiency. However, the trend of CO, emission of unit A, is consistent with that of other units, i.e., an increasing CO, emission with increasing efficinecy. Thus, among * this group a slightly different trend is emerging between the boiler capacity, efficiency and pollution emission (though a consistency is observed among the CO, values) (Table 5.3) Conclusion The result of the above analysis clearly help to bring in to the focus the following observations. (1) Boiler technology (type of boilers) remaining constant more the design capacitymore the energy efficiency. (2) More the energy efficiency less the emission of SO,, NO, and SPM and more the emission of CO,. (3) The boiler type (technology) remaining constant coal gives more efficiency and less SO,, NO, and SPM pollution and more CO, pollution compared to lignite. (4) Technology remaining constant, lignite as energy input emit almost double the quantity of SO,, NO, and SPM pollution and half the quantity of CO, pollution, though the energy efficiency is less compared to coal. 169

21 (5) Among the different boiler technology types FBC boilers have the highest cumbustion efficiency (79.79% when coal is used as fuel import) and lowest emission of SO,, NO, and SPM, and highest emission of CO,. The package boiler is less efficient (73.34% when coal is used) than FBC boilers, and lancashire boiler is still less efficient (54.51% when coal is used) than package boilers. (6) Though there is a significant difference in pollution emission between package and FBC boilers, the cumbustion efficinecy variation is having much less difference. (7) Technology remaining constant more efficiency is realized when coal is used as fuel input than when lignite is used as fuel input. (8) The specific fuel consumption (when coal is used) per ton of steam generated is, lowest in case of FBC boilers having high design capacity and highest in case of lancashire boilers having low design capacity. (9) The lowest cost of steam generation (hence, highest steam economy) is observed with FBC boilers (when lignite is used as fuel input) and highest cost of steam generation (hence, lowest steam economy) is found among the lancashire boilers (when coal is used as fuel input). (10) The lowest cost of steam generation is experienced in all types of boiler technology when lignite is used as fuel input. (11) The highest steam economy is realized when high capacity FBC boilers operate on lignite and lowest steam economy is realized when low capacity lancashire boiler operates on coal. (12) The lowest SPM, SO, and NO, pollution emission is found when FBC boilers use coal, and the highest pollution emission ofthese parameters is found when lancashire boiler combust lignite. 170

22 (13) When there is a significant efficiency variation between lancashire and package boilers, the pollution emission of both the boilers are almost same. The above comparative analysis provides a definite indication that lancashire boilers are inefficient in terms of energy benefit. A disturbing result emerges in terms of its total pollution emission and environmental implications. At the same time FBC boilers are providing more thermal efficiency and lowest pollution emission in terms of S02, NO! and SPM and maximum pollution emission in terms of CO,. The package boilers are having a combustion efficiency which is almost nearer to FBC boilers but are having much more pollution emission than FBC boilers and equal pollution emission compared to lancashire boilers. Therefore, the available experimental evidence shows that the FBC boiler technology is more beneficial Jjoth in terms of energy efficiency and pollution mitigation/avoidance (if the initial investment needed and the payback derived is not the prime consideration in the short run, compared to package boilers about which the next Chapter deals with). 171

23 Table 5.1 Flue Gas Analysis of Lancashire Boilers Name S Code of the Unit Fuel used Design capacity of the boilers (TPH) Operating capacity of the boilers : Fuel consumed Specific Fuel consumption per tone of steam generated (Tons) Steam cost based on fuel consumed (TPH)/RS, Flue Gas Analysis (Energy Efficiency Parameters Fuels) IC02 CO (PPM) Tempera ture A1 Coal El Coal Cl Coal D1 Coal f,-f.. A2 Lignite B2 Lignite C2 Lignite D2 Lignite