Power Generation Using Biomass Fuel

Conference paper

Power Generation Using Biomass Fuel John H. Pohl (Energy International, Laguna Woods CA, USA 92637), Terry F. Dixon, (MyLec, Brisbane, QLD, Australia), and William Gilfillan (Technical University of Queensland, Brisbane, QLD, Australia) ABSTRACT Biomass has recently been recommended as a sustainable fuel that can replace fossil fuels and reduce the emissions of green house gases (CO2 and CH4). However, biomass must met two criteria to be successful as a fuel: 1) it must be technically feasible and 2) it must be economic on a life cycle basis. Biomass fuel has been proven to be technically feasible, but the economics of its use are still in doubt. This paper presents the work done by the authors on a number of biomass fuels in several countries. This work has ranged from reports on the combustion properties of the fuel based on the ASTM analysis, to pilot scale evaluation of combustion properties of the fuel, to evaluation of commercial operation of an electrical generating facility. Investigation of a number of different biomass fuel are reported in this paper. The fuels vary from sugar cane waste (bagasse and trash (material left in the field)) form Australia; biomass to be burned on 1000 islands in South Korea; tequila bagasse, paper and cardboard waste to be burned in Mexico; coconuts shells and coir (hair on the outside of the shell) to be burned in the Philippines, and saw mill waste, municipal solid waste gases, and lumber waste to be burned in the US. The work ranged from evaluating the combustion properties of biomass from ASTM analyses for South Korea, Mexico, the Philippines, and the USA, to municipal solid waste (MSW) including work done on an existing commercial power generation plant in the US, Puente Hills Landfill Plant; design and construction of a pilot scale unit to determine any combustion problems with sugar cane waste in Australia. The only biomass combustion facility that made life-cycle ( economic of growing, harvesting, transport, preparation, burning, clean-up, and waste disposal) was the one burning municipal landfill waste gases. This plant paid-off the investment in two years (ROI~50%) and was returning $2 MM/yr. The other biomass close to make life-cycle economical sense was sugar cane waste. In reviewing the life cycle costs of generating electricity from sugar cane waste, we reviewed 20 uses of biomass in 12 countries, Dixon, et al. (1998). In this case, sugar cane is grown to produce sugar from the cane in a sugar mill, the sugar cane bagasse is the casing surrounding the sugar cane and is transported on a narrow gage railroad to the sugar mill. The bagasse is removed from around the sugar cane and is usually burnt inefficiently to produce heat for the sugar mill. So in the case of sugar cane, the waste from the sugar cane is grown and transported #12;to the mill for sugar production. The is trash left in the field, so it has costs to be collected and transported from the field to the mill and prepared. The cost to be considered are the collection, transport. and preparation of the trash costs at the mill and clean-up and disposal costs of the waste products. The cost of generating electricity from sugar cane waste at 35% efficiency was about 4.2 Australian cents/kWe-hr compared to about 3.5 Australian cents/kWehr for coal. The captial cost of biomass plants is shown in Fig. 1, Dixon, et al. (1998). The cost of the plants is between $1000. Aus/Kwe to $2500 Aus/Kwe compared at the time to about $700 Aus/Kwe for a coal-fired plant. INTRODUCTION Many countries are proposing biomass be used as an alternative to fossil fuels. Use of biomass fuels will replace the limited amount of fossil fuels available and reduces the amount of greenhouse gases (CO2 and CH4) released into the atmosphere. A biomass fuel will eventually decomposed into CO2 and CH4, so generating energy and heat from biomass fuels used to replace fossil fuels will reduce the amount of greenhouse gases (CO2 and CH4) released into the atmosphere. The remaining question, is biomass a cost effect substitute for fossil fuels. The cost needs to be evaluated on a life cycle basis. Of the fuels the authors have studied very few make life cycle economic sense. BIOMASS FUELS STUDIED A number of biomass fuels were studied to different extents by the authors. Some fuels were evaluated based on their ASTM test results, some were evaluated using pilot scale tests, and a few were evaluated in commercial operations. WOOD Wood in several configures was evaluated at several different level of used. The wood varied from sawmill waste to lumber waste. Sawmill Waste Saw Mill waste was burned at a lumber mill in Washington state, USA. This particular use of biomass proved not to be questionable economically. Lumber Waste Lumber waste from a Marine Base in North Carolina was analyzed for use as a bio-fuel. The ASTM analysis showed this fuel had the characteristics to be within acceptable standards for combustion. Wood fuel usually has a moisture contents approaching 60 %, low ash contents of #12;several percent; with high contents of alkali materials-particularly K2O (~$4%); and low heating value (about less than half that of natural gas). This wood biomass fuel showed it had a high cost relative to fossil fuels. VEGETABLE WASTE Vegetable waste was evaluated in four cases, Coconut shell and Coir from the Philippines, Tequila Bagasse from Mexico, vegetable waste in Korea, and Sugar Cane Waste in Australia. Most of these fuels were evaluated using ASTM analyses results. Sugar Cane Waste was evaluated in a pilot scale combustor. Coconut Shells and Coir We analyzed coconut shells and coir (hair like material outside the coconut) and other vegetable waste using ASTM procedures. The ASTM analysis showed this fuel to be acceptable as a replacement for fossil fuel. The estimated cost of the fuel was not competitive with fossil fuels. Tequila Bagasse Tequila bagasse is the vegtable matter surrounding the plant material that is processed to produce tequila. We performed ASTM analysis on tequila bagasse and Cardboard waste from Mexico. The ASTM analyses showed no apparent problems with burning of these fuels, but we recommended that further analyses of the life-cycle economics are required before these fuel can be accepted for commercial use. Biomass for 1000 Korean Islands I discussed use of Biomass to generate electricity on 1000 Korean Islands. In Korea the cost of electricity is regulated to be uniform for all of Korea. The islands have limited population and resources so the cost of generating electricity is expensive on the islands. We concluded that there was nothing obviously precluding use of biomass other than cost. Sugar Cane Bagasse and Trash Use of Sugar cane bagasse and trash (material left in the field) was examined as a replacement fuel for coal-fired electricity generation, see Photograph of Sugar #12;Cane Waste in Fig. 2. The location of sugar mills in Australia is mostly on the north-east coast of Queenslands and in Northern New South Wales, see Fig. 3. This study analyzed the sugar cane waste fuel using ASTM Analyses as shown in Figure 1. The results are shown in Table 1. and 2.. A semantic of the electricity generating system proposed is shown in Fig. 4.. Additionally, investigation was performed in a pilot scale combustor. These waste material, see Figure 1., are traditionally burned in a furnace with the fuel falling by gravity onto a burning bed and finishing burning on a fixed bed, (see Fig. 5). The pilot scale combustor is shown in Fig. 6. Fig. 6. shows a photograph of proposed design of the pilot scale combustor. Fig. 5. shows the velocity profile used to fluidize the particles The fuels are burned inefficiently to generate heat and raise steam for processing sugar cane into sugar. Pilot Scale Combustion Facility for Sugar Cane Waste A pilot scale combustor for sugar cane waste must first match the timetemperature profile of the full size combustor. This is accomplished by insulating the pilot scale unit so that the temperature profiles match as is shown in Figure 6. The velocity in the pilot scale furnace must be reduced to give proper scaling of the time to match that of the full sized commercial furnace. This is more difficult in a fluidized bed than in a combustor with near plug flow patterns. Figure 5. shows the gas velocity in the pilot scale combustor and compares the velocity with the velocity required to float a percent of particle that would be fluidized at specific velocities in the pilot scale furnace. DESIGN of PIOLT SCALE FURNACE The sugar cane commercial furnace uses a combination of a fluidized bed and a fixed bed combustor. Fig. 6. shows the heat transfer surfaces in the pilot scale combustor. Figure 7. and 8. show the inserts used to measure slagging and fouling. These devices are inserted in the furnace in the same temperature region and at the same velocity at which slagging and fouling occur. The deposit build up is measured as it occurs and is measuring by the decrease in heat transfer with time at the same surface temperature as the actual combustor. The surfaces can #12;be withdrawn and the thickness of the deposit measured using electron microscope and/or an optical microscope. CONCLUSIONS Eight biomass fuels have been evaluated at different levels. Saw mill waste was investigated at a saw mill plant. Lumber waste was studied at a military base. Biomass from 1000 Korean Islands was discussed with a Korean energy company. Tequila Bagasse and Coconut Shells and Coir was investigated using ASTM chemical analyses. Landfill gas was investigated at a commercial plant generating electricity. Sugar cane waste was investigated in a pilot scale combustor. Few of the investigated biomass fuels proved to be commercially feasible. The one that did was the commercial plant (Puente Hills Landfill Site) which was generating electricity. This plant took the off gas from Landfill and burned the gas in a boiler. This plant paid off the investment in 2 years (ROI~50%) and was returning about $2 million/yr. The other biomass plant that came close to being economically feasible was the fluidized bed-fixed bed combustor used to burn Sugar Cane Waste and generate electricity. This plant generated electricity at 35 % efficiency for about 4.5 Australia cents/Kwe-hr compared to about 3.5 Australian cents/kwe-hr for a coalfired boiler. #12;Fig. 1. Capital Cost of Bomass Power Plants, Dixon et al. (1998). #12;Fig. 2. Photographs of Sugar Cane Waste, Gilfillan (2001). #12;Fig. 3. Location of Sugar Cane Mills in Australia (Dixon, et. al (1998). #12;Table 1. Ash Fusion Temperatures for Sugar Cane Bagasse. Property Temperature Ash Deformation 1218 oC (2224 oF) Softening 1302 oC (2376 oF) Hemispherical 1372 oC (2376 oF) Fluid 1480 oC (2696 oF) #12;Table 2. ASTM Analysis of Natural Gas, Sugar Cane Bagasse, and Sugar Cane Trash. PROPERTY HARVEST RESIDUES NATURAL GAS BAGASSE (typical) (data from SRI) (data from SRI, Reisinger 1996) -- 50 20 - 50 -- 5 10 -- 77 ~80 47.5 19.65 17 74.2 50 49.5 H2O % (wet basis) Ash % (dry basis) Volatile Matter (daf)% HHV (daf) MJ/kg C (daf)* #12;22.45 6 H (daf) 6 0 43.7 44 3.35 0.3 0.5 4 0 0 O (daf) N (daf) Cost $A/GJ #12;Figure 4. Semitic of Pilot Scale Furnace to Test Burn Sugar Cane Waste. Gilfillan (2001) #12;i Fig. 5. Particle Velocity Profiles, Gilfillan (2001). #12;Figure 6. Temperature Profiles in The Pilot Scale Furnace. Gilfillan (2001). #12;Figure 7. William Gilfillan Beside Pilot Scale Combustor during Construction. Gilfillan (2001) #12;Figure 7. Pilot Scale Slagging Probe. Gilfillan (2001). #12;Figure 8. Pilot Scale Fouling Probe, Gilfillan (2001). #12;References Dixon, T.F., P.A. Hobson, J.A. Joyce, J.H. Pohl, B.R. Stanmore, and C. Spero, Electricity Cogeneration and Greenhouse Gas Abatement in the Sugar Industry, Queensland Biomass Energy Group, Queensland, Australia (1998). Gilfillan, W.N., Design of a Laboratory Rig to Determine Slagging of Biomass Fuels, University of Queensland Department of Chemical Engineering, MEngSc, Brisbane, Queensland, Australia (2001).