calcium and potassium sulphate deposits in low temperature regions (below 982 oC - 1800 oF) of the boiler when cofired. The conclusions drawn from the PCQUEST modeling and FACT calculation results were as follows: c No significantly increased high temperature fouling or slagging would occur at any blend level of the lignite coal with the tree wood or the wood chips, and increasing the amount of biomass cofired with lignite generally provides slight improvement in fireside performance c The changes in predicted fouling, slagging and opacity vary directly with the amount of biomass in the blends, with no 'optimum' blend level c Opacity and low temperature fouling behaviour may only be moderately adverse at very high biomass blend levels (80% biomass or greater) c The general linear PCQUEST and FACT results in relation to biomass blend level resulted in the selection of a 50% lignite coal - 50% biomass blend for the combustion tests to generate high temperature fouling deposits. This blend level would allow interpolation to lower blend levels suitable for large power generating plants as well as extrapolation to higher blend levels in stoker boilers. A blend level of 25 % lignite coal - 75 % biomass was selected for the grate clinkering tests. million through a municipal 20-year bond at 5% interest for the required capital investment of the project. A cash flow analysis indicates the bond could be paid off in 15 years with advanced payments from the savings. Energy costs are escalated based on typical values used by the state legislature for energy performance contracts. Natura! gas, electricity and cola rates are $5.18/million btu, $0.05/kWh, and $21.41 per tonne ($19.42) respectively. O&M includes labour for individual operators at $31200 per year, replacement parts, chemicals, ash disposal and fuel system maintenance at $ 1.10/tonne ($1.00 per ton). UNIVERSITY OF NORTH DAKOTA - COFIRING USING BIOMASS AND SUB-BITUMINOUS COAL The UNO, located in Grand Forks, NO, operates a steam facility that currently fires 45360 tonnes/year of sub-bituminous coal, providing 79000 MJ/hour (75000 btu/hour) of 896 Mpa (130 psig) saturated steam to the campus. The types of biomass being considered for cofiring include sunflower hulls, turkey manure, sawdust and municipal wood. The most significant resources in terms of quantitiy are sunflower hulls and sawdust, at over 45.360 tonnes/year each. Turkey manure and municipal wood are available at less than 50% of UNO's total consumption. Most likely UNO will choose to fire sunflower hulls This level would best represent the stoker boiler operation proposed for the NOSP, where high biomass blend levels produce desirable economics. TABLE 3. Correneration svstem performancc Turbine e.enerator nerformance Peak load 784 kW Condensinıı turbiııe heat rate 17.2 k!!llıour/kW Task 4 - environmental issues Backnressure turbine heat rate 86 k<'llıour/kW Pressure reducinıı turbine heat rate 20.4 kg/bour/kW Gross annual electricity (100% availabilitv) 5.854.883 kWh Load factor 1 Load 784 kW Availabilitv 90% Parasitic losses 15% Net anııual electricity 4.478.985 kWlı Ali environmental requirementswere investigated relative to implementing cofiring and cogeneration. No significant technical or economic impacts from permitting activities will occur. Estimates on emissions have been calculated (unfortunately lack of space does not permit their publication here). Boiler nerformancc Sıeam suoolv consisteııt output 1 1.300 kıı/h Steam heat rate 26.750.000 btu/hour Boiler efficiency 72% Firin<' rate 37. 1 52.778 btu/hour The choice for cogeneration will be to install both a condensing and a backpressure turbine at the facility. Although the payback on the backpressure unit is marginal, a used unit will provide flexibility, and redundancy to help improve plant availability. Also small pressure-reducing turbines will be integrated at distributed locations where steam flow is relatively hig to make use of energy that is otherwise wasted by a pressure reducing station. Fuel requirements Moistııre content Ratio Task 5 - economics The following case represents a 75% biomass - 25% coal cofiring cogeneration scenario. The planı would operate 11 months of the year at full load steam output. The fuel supply is 14.515 tonnes per year of municipal wood, which is within estimated recources, but about twice what was conservatively confirmed in the resource assessment. The coal consumption is 4536 tonnes per year and about twice what NOSP currently consumes. An estimated three truckloads per day will be required, which is well within reasonable traffic rates for the NOSP site. For an attractive projeci, the intention will be to finance $1.68 40 ij ECOGEHERATIOH WDRLD H.HV coal 36.8% 25% 14.800 btu/kg HHV biomass 7.3% 75% 18.265 btu/kg Fuel flow drv coal 29% 630 kg/lıour Fuel flow dry biomass 71% 1526 k0ihour Tonnaı:,e reQuired, coal 36.8% 25% 4957 tonoes/vear Toıınage required, 25% 75% 14.883 tonoes/year biomass Truckloads wood oer vear (a). 18 tonoes/load 820 truckloads Truckloads wood per day@ 240 days/year 3 truckloads/day or sawdust based on delivered costs in the range of$ 16.5327.55/tonne ($15-25 ton). By comparison, cola is $33/tonne ($30 ton).Municipal wood presents fuel preparation and handling difficulties, and turkey manure -despite the attractive low cost- presents odour-control issues. UNO has completed a test burn of sunflower hulls and sawdust under this programme. Oata were collected concerning handling issues and combustion performance, which could affect the percentage of biomass cofired. The economic target is to achieve less than five-year payback on investment.
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