Performance Analysis of Gasifier during Co-firing using Biomass and Lignite for Power Generation

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1 Available online at International Journal of Innovative and Emerging Research in Engineering e-issn: p-issn: Performance Analysis of Gasifier during Co-firing using Biomass and Lignite for Power Generation N. Harindranath 1, Dr. R. Suresh 2, Dr. Y. Jagannada Rao 3 1 Research Scholar, Department of Chemical Engineering, R.V College of Engineering, Bangalore-India. 2 Professor, Department of Chemical Engineering, R.V College of Engineering, Bangalore-India. 3 Professor, Department of Chemical Engineering, Siddaganga Institute of Technology, Tumkur-India ABSTRACT: Co firing is the simultaneous combustion of a supplementary fuel with a base fuel to increase efficiency and capacity of the gasifier plant. Cofiring was seen as a work for reducing greenhouse gas emissions. In the present work open top downdraft biomass gasifier of capacity 100 KW was set up and used. The eucalyptus wood was used as a primary fuel and the lignite obtained from Neyveli was used as a secondary fuel in this gasifier Wood to lignite ratios of 98:2, 95:5, 92:8, 85:15, and 80:20 by weight were mixed manually and charged into the reactor. The effect of variation of temperature along the length of reactor, composition, calorific value, flow rate of the gas generated at different co-firing ratios of wood and lignite was studied. The use of this syngas for power generation and cold and thermal efficiencies of the process were also studied. These results are presented. Keywords: Cofiring, Biomass, gasifier, lignite, power generation I. INTRODUCTION Co firing is the simultaneous combustion of a supplementary fuel with a base fuel. Selectively, utilities and independent power producers have used biofuels, particularly wood waste to generate electricity in small stand alone generating stations with less than 50MWe capacity. In more recent years, utilities have become interested in co firing biofuels with coal and other fossil fuels, applying wood wastes and other solid forms of biomass to high efficiency, higher capacity generating plants [1-5]. Initially, co firing was seen as a means for from reducing greenhouse gas emissions fossil energy generation. Biomass co firing with coal is proving to be the cheapest method for generating green power in utility plant demonstrations [6-11].Co-firing facility is less sensitive to seasonality in biomass production and to biomass availability and price. The potential for expanding the use of biomass energy technologies for energy generation is vast in India and awaits further exploitation. In this context, biomass co firing and its applicability to Indian power production will be a great boost to the power producers, environmentalists and all concerned [12]. II. EXPERIMENTAL In the present work open top downdraft biomass gasifier of capacity 100 KW was set up.the details of the set up and procedure for its operation were discussed recently elsewhere [13]. One of the major advantages of this type is that the syngas has to pass through the hot combustion zone before it leaves the gasifier. By this passage the tar takes part in the combustion or is decomposed to light hydrocarbons, and the outgoing gas is under ideal circumstances tar-free. When using this gasification technology, the gas is directly usable for running engines after soot and ash particles have been washed out. The gasifier is coupled with a suitable cooling and cleaning unit. The blower is used to create required suction to draw the gas. The temperatures at various locations inside the reactor were recorded using calibrated K-type (Inconel) thermocouple which is connected to the digital temperature indicator. Flow rate of producer gas was measured using a calibrated venturi meter. The chemical compositions of syngas were measured using a Gas Chromatograph equipped with a Thermal Conductivity Detector and a 32 BIT Data Acquisition Software for O 2, H 2, CO 2, CO, CH 4 and N 2.The power was generated using syngas by Cummins Engine (100 KVA).The overall efficiency of the biogasifier plant was computed for each condition and the remnants of gasification were weighed using a balance. III. RESULTS AND DISCUSSION The eucalyptus wood was used as a fuel for wood gasifier. It consists of cellulose, hemicelluloses, and lignin in the ratio of 43%, 35% and 22% respectively The approximate composition of wood is about 75 to 80 % volatile and 20 to 25 percent fixed carbon. The wood pieces of size 50 mm length and 50 mm diameter were cut using a wood cutting machine to form wood chips, wood pellets and saw dust. Then it was dried in sun light for a period of a week or until moisture was 1

2 Temperature, C International Journal of Innovative and Emerging Research in Engineering completely eliminated from the biomass. It was then stored in the dry room. Moisture in the biomass can also be removed within the drier room using the hot exhaust gas from Cummins gas engine. This biomass was used as a primary fuel and the lignite obtained from Neyveli was used as a secondary fuel. Initially wood alone was fired in the reactor for about 8 hrs a day continuously for 4 days. Then wood to lignite ratios of 98:2, 95:5, 92:8, 85:15, and 80:20 by weight was mixed manually and charged into the reactor. The effect of variation of temperature along the length of reactor, composition, calorific value, flow rate on different co-firing ratios of wood and lignite was studied and results are discussed below. A. Effect of co -firing ratio on temperature distribution The temperatures at various heights inside the reactor were recorded using thermocouples (Inconel 600, < 1200 ºC 5 ºC).The total length of the reactor is 3.2 m. Diameter of the thermocouple is about 6 mm and length is 3 m. The Thermocouple has a digital temperature indicator. It is positioned vertically inside the reactor. Then the thermocouple is moved in steps of 20 cm, and the temperatures are recorded accordingly. These results of temperature distribution as a function of length of gasifier are given in Table 1 and shown in Fig. 1. Table 1. Temperature at various co -firing ratios Co-firing ratio Temperature in ºC Length of the Gasifier in m : : : : : R Zone C Zone P zone D zone Height of the reactor, m Fig.1. Temperature distribution as a function of height of the reactor The temperature distribution curve can be divided into four zones namely Reduction zone (R zone), combustion zone (C zone), pyrolysis zone, (P zone) and drying zone (D zone) as shown. In drying zone heat was mainly from the pyrolysis zone by radiation and convection. The biomass is dried and most of the moisture is driven out as water vapor. There is no significant difference in temperatures for wood and wood-lignite blended fuels in this zone. In the pyrolysis 2

3 zone thermal decomposition of fuel takes place at temperatures above 400 C for wood and wood/lignite blended fuels. The average temperature of this zone is around 500 ºC for all type of fuels. In the pyrolysis zone all volatile materials are burnt out. It is seen that the temperature for wood in this zone is greater than that for other co-firing ratios due to higher volatile materials present in wood fuel. In other words, the pure wood curve shows the lowest temperature in R and C zones but it is relatively higher in P zone. It shows that heat energy is consumed by wood for pyrolysis whereas in the presence of lignite the temperature is relatively lesser and this energy manifests in the combustion zone. All five types of fuels (pure wood and lignite-wood blends) show the maximum temperature in C zone only with different magnitude. The reaction between carbon and oxygen is responsible for high temperature in the combustion zone. The combustion temperature increases with increasing lignite content. The maximum temperature is seen for 20% lignite blended fuel. As per Van Krevelen diagram [14] higher the oxygen content of fuel, lower is its heating value. Wood has higher oxygen / carbon ratio than that of lignite hence the lignite blended fuels show the maximum temperature in this zone. In the reduction zone following reactions occur. The remains are ash and some char (unburned carbon). The gas exits from the bottom, and the outgoing gas under ideal conditions is tar-free. The temperature of wood C is seen between 0 to 0.22 m height and C seen between 0.22 to 0.34 m. In the reduction zone there is a clear recognizable pattern of increase in temperature with the increase in lignite content. B. Effect of co -firing ratio on composition of the exit gases The exit gases from the gases were analyzed and their compositions obtained for different co-firing ratios are given in Table 2 and shown in Fig 2. Table 2. Composition of syngas for various co-firing ratio of lignite / wood fuels Syngas % of Lignite ( Co-firing ratios) Composition O N CO CH CO H It is seen from the figure that the oxygen and nitrogen show similar trend of increase in volume with the increasing lignite addition. It is seen clearly that the hydrogen and methane production is highest for 8% lignite blended fuel and a minimum for wood. Carbon monoxide shows highest production for wood and relatively lower values for other blends. 3

4 % of gas by volume International Journal of Innovative and Emerging Research in Engineering % of Lignite (Co-firing ratio) Fig. 2. Composition of syngas for various co-firing ratios. C. Effect of co -firing ratio on calorific value of the exit gases The heating values of the syngas for various co-firing ratios of lignite and wood is computed by taking into account the composition of the combustible components namely CO, CH 4 and H 2. The formula used is HV of syngas = Sum [(x1) (HV1) + (x2) (HV2) + (x3) (HV3) +...] HVn = heating value of gas component n, in kj/m 3 x = mole fraction of gas component n The calorific values obtained for different compositions (co-firing ratios) are given in Table 3 and shown in Fig 3. It can be seen that the 8 % lignite blend shows maximum heating value of syngas and the blends up to 15 % show relatively higher heating values than that for wood. Table 3. Calorific values of exit gases at different co-firing ratios % Lignite(Co firing ratio ) Calorific value MJ/m

5 Calorific value of syngas, MJ/m 3 Percentage of lignite in the lignite-wood fuel blend Fig.3. Calorific value of syngas with varying co-firing ratios D. Effect of co -firing ratio on power out put and gas flow Flow rate of producer gas was measured using a calibrated venturimeter. A manometer is connected across venturimeter to measure difference in pressure between the upstream and downstream pressure taps. Gas flow rate is calculated using the equation. Gas flow rate g/s = k x p 1, where p 1=differential pressure across the venturimeter (mmwc) and k=venturimeter constant and its value is 7. The power was generated using syngas by Cummins Engine (100 KVA). The syngas was fed according to the load requirement and then sent to the gas engine with air fuel ratio (13:1) Engine was coupled to alternator to convert electricity at 400v and power generated was connected to the grid. The values of flow rate and power generated at different co-firing ratios are given in Table 4 and shown in Fig. 4. Table 4. Power output and syngas gas flow for co-firing ratio S No. Lignite Gas flow Power, kw g/s 1 0% % % % % %

6 flow rate g/s power kw Co-firing ratio (% Lignite) Fig.4. Effect of co-firing ratios (%lignite) on power output and syngas gas flow rate It is observed from the results that the flow rate of syngas yield and power output depend upon many factors like temperature, moisture content input power. It is clear from the figure that gas flow rate increases with increase in the lignite content up to 8% and decreases with further increase in lignite content but there is not much change in power output. It is observed that the gas flow rate and power produced are optimum for 8% lignite blended fuel. E. Effect of co -firing ratio on feed rate and wastage Experiments were conducted with different feed rates and varying the co-firing ratios and wastage which was weighed using a balance.the results are given in Table 5 and shown in Fig 5. It is observed that the feed rate and wastage values depend on the parameters like temperature, moisture content and feed size. As per the results feed rate is almost constant at biomass and lignite ratios of 0% and 2% blended fuel. The feeding rate gradually decreases with increase in lignite content due to the increase in temperature. Table 5. Power output and syngas gas flow with different co-firing ratios S No. Lignite % (co-firing ratio) Feed Rate Kg/hr Wastage Kg/hr

7 wastage feed rate % Lignite (co-firing ratio) Fig.5. Plot of feed rate and wastage vs co-firing ratio It can be seen from Fig 5 that the wastages is constant up to 5% blended fuel and wastage suddenly decreases at 8% blended fuel and then remains constant at 15% and 20 % of lignite. F. Effect of co -firing ratio on Cold gas and thermal effeciencies Thermal efficiency is the ratio of power output and power input.they are obtained using the following equations Gasifier power output = 3 x V x I COSӨ V= voltage and I= current COSӨ = power factor and its value is 0.8 Input power Q a =M f x C vf HgxQg Thermal efficiency is given by HsxMs H g = Heating value of gas kj/m 3 Q g= volume flow of gas m 3 /s Hs= lower heating value of gasifier fuel kj/kg Ms=gasifier solid fuel consumption kg/s Cold gas and thermal efficiencies are calculated and given in Table 6 and shown in Fig 6. Table 6. Cold gas and thermal efficiencies for co-firing ratios S No. Lignite % (Co-firing ratio) Cold gas efficiency Thermal efficiency 1 0% % % % % %

8 Efficiency International Journal of Innovative and Emerging Research in Engineering Cold Gas efficiency Thermal efficiency % of lignite(co-firing ratio) Fig 6. Cold gas and Thermal efficiency for the co-firing ratio It is observed that the cold gas efficiency increases with increase in lignite content. It is seen that thermal efficiency increases with increase in lignite concentration up to 8% reaches maximum and there after remains constant with further increase in lignite content. IV. CONCLUSIONS Cold gas efficiency increases with increase in lignite content. It is seen that thermal efficiency increases with increase in lignite concentration up to 8% reaches maximum and there after remains constant with further increase in lignite contentdecide what to write here. ACKNOWLEDGMENT I hereby acknowledge my Mother Late NAMBAKKAM SAROJINAMMA for her great contribution in inspiring me to achieve professional excellence. REFERENCES [1] Ekmann JM, Winslow JC, Smouse SM and Ramezan M., International survey of co-firing coal with biomass and other wastes, Fuel Process Technol., 54:71 88, 1998 [2] Harding NS and Adams BR., Biomass as a reburning fuels a specialized co firing application Biomass Bioenergy, 19:29 45, 2000 [3] Ross AB and Jones JM., Measurement and prediction of the emission pollutants from the combustion of coal and biomass in a fixed bed furnace, Fuel, 81:571 82, 2002 [4] Sami M, Annamalai K and Wooldridge M., Co-firing of coal and biomass fuel blends, Progr Energy Combust Sci., 27:7 23, 2001 [5] Skodras G and Grammelis P., Emission monitoring during coal waste wood co-combustion in an industrial steam boiler, Fuel, 81:547 54, 2002 [6] Narayanan KV, Natarajan E. Experimental studies on cofiring of coal and biomass blends in India. Renew Energy (2007), doi: /j.renene [7] Battista J, Hughes EE and Tillman DA., Biomass co-firing at Seward station, Biomass Bioenergy, 19:419 47, 2000 [8] Changqing Dong, Baosheng Jin, Zhaoping zhaong and Jixiang Lan, Tests on co-firing of coal and MSW in a circulating fluidised bed, Energy convers manage., 43:189 99, 2002 [9] Hughes E and Tillman DA. Biomass co-firing: status and prospects, Fuel Process Technol., 54:27 42, 1996 [10] Hus PJ and Tillman DA, Co-firing multiple opportunity fuels with coal at Baily generating station, Biomass Bioenergy, 19:385 94, 2000 [11] Tillman DA, Co-firing benefits for coal and biomass Biomass Bioenergy, 19(6), 2000 [12] Yoshikawa, K.and Moritsuka,H., Advanced technologies for biomass power generation. CMC Press, Japan, 2006 [13] Harindranath,N.,SureshR., and RaoYJ,, Optimization of biomass gasification for power generation, Int.J of informative and futuristic research, 2(10)3721, 2015 [14] Tillman D.A, Biomass co firing: the technology, the experience, the combustion consequences, Biomass and Bioenergy, 19, ,