Task 1 • resource assessment This task was carried out in a very similar fashion to the NDSP project. However in this case, agricultural processing residues were of significant interest, due to the high amount ofprocessors located within 160 km. (100 miles) The most promising resources identified, in order of preference were sunflower hulls, turkey manure, landfill wood and sawdust. The available quantities are as follows: c sunflower hulls - 40.824 tonnes/year c turkey manure - 22.680 tonnes/year c landfill wood - 7258 tonnes/year c sawdust - 221,357 tonnes/year The sunflower hulls proved most promising because of their superior relative quantity (equivalent to UND's existing capacity), quality (equivalent heating value to coal), ease of handling and low delivered cost- $16,53/tınne ($15/ton). Task 2 • fuel handling issues A feed system was designed to handle both sunflower hulls and sawdust. The general arrangement consists of a receiving station, grinder, screen and aerated storage silo. UND uses coal cars with bottom dumps. The design for mixing and feeding biomass into the system is to operate a speedcontrolled auger from a separate biomass storage silo. This auger will feed material under gravity fed pits from the coal cars. Coal and biomass will then mix and be fed into the existing coal feed system. This simple arrangement utilizes existing equipment and minimized the capital investment for implementing cofiring. Task 3 • fireside issues in order to address fireside issues, a test burn was completed at the UND facility. A 25% biomass, 75% coal mix (by weight) was fed in a single boiler at low-, medium- and full-load capacities. Data was collected on emissions and or a blend of coal and biomass, typically has a beneficial impact with regard to stack emissions. Most biomass resources are low in sulphur, and resul! in substantially lower SO2 emissions for the same fuel input. Biomass typically has lower ash content, resulting in lower amounts of uncontrolled particulate emissions; however, the particulates generated from burning biomass are typically tiner than coal ash and may or may not lead to lower stack emissions. When burned wet, biomass will also reduce flame temperatures during combustion, and can produce lower levels of Nox. Task 5 • economics The economics of cofiring sunflower hulls at UND are quite attractive. This cofiring scenario assumes a cofiring rate of 25% sunflower hulls by weight. This requires about 10.886 tonnes/year of biomass, which is only 25% of the amount produced by the closest processor. The required capital investment to install a storage silo, purchase a used tractortrailer for transportation, and fuel conveying equipment is $408.771. The savings generated can pay back a 10 year bond financed at 5,25% in five years with advanced payments from the savings. The energy cost savings, accounting for additional O&M, is about $100.000 per year. Actual savings after debt service are approximately $50.000 per year. CONCLUSIONS There is a tremendous opportunity to increase the use of biomass through cofiring. Facilities that have already invested in fossil fuel energy infrastructure can cofire biomass with limited investments in process modifications. The projects described in this article provide case studies that can be utilized by others to determine how to approach potential projects. it is of paramount importance to realize that the economics of using biomass can be marginal in many applications. The investigator must take signifıcant measures to ensure attractive return on investments. operating conditions. These tests NOx emlaılona dala The key components include the following: 400 . Coal #3 350 ·Mix#3 300 250 � 200 a.. 150 100 50 c A comprehensive biomass resource assessment focusing on quantity, cost, quality, reliability and availability of the local resources were run to verify necessary capital investments. The boiler conditions were not optimized for biomass-firing, in order to determine what adjustments would have to be made relative to sub-bituminous coal-firing. The results of the emissions are shown in Figure 2. No clinkers or excessive fouling were observed. However, it was quite obvious that the less dense biomass particles would react almost completely in suspension. Necessary adjustments to boiler to optimize firing of the sunflower hulls will include slowing of grate speeds in order to maintain a protective layer of ash on the grate, and an increase in overfire air rates from 15% to 40%. O+----��-�-�---�� c Fuel transportation, handling and feeding design, focused on minimizing capital investment, integrating with existing infrastructure and proper design for difficult biomass fuels Task 4 • environmental Switching fuel from coal to biomass, l2 ECOGENERATION WORLO o 10 600 . Coaı #3 500 •Mix #3 400 ::ıı 300 a.. a.. 200 100 20 30 40 50 60 Load (thousands) SOx emlaalona dala y = 0.0066x + 94.523 A2 = 0.9533 • •• R2 = 0.7994 70 80 o -ı.--��-�-�-----�� o 10 20 30 40 50 60 70 80 Load (thousands) FIGURE 2: Emissions from test burn (upper curve is baseline coal, and lower curve is 25% sunflower hull mix) c Actual firing tests to ensure proper boiler modifications c Economic anaylsis. With the proper integration of these factors, the benefits of reduced emissions, landfill diversion and potential economic development can be realized. Source: Cogeneration and On-Site Power Production
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