Biomass Based Power in Alberta

Transcription

1 Biomass Based Power in Alberta Amit Kumar, Jay B. Cameron, Peter C. Flynn Department of Mechanical Engineering, University of Alberta, Edmonton, Alberta, Canada T6G 2G8 Abstract This study estimates the cost of biomass power in the Province of Alberta. The biomass power cost and optimum size of the power plant is estimated for three fuels: whole forest (trees in the form of wood chips), forest harvest residues (logging residues, i.e. chipped limbs and tops) and agricultural residues (straw). Optimum biomass power plant size is a tradeoff between increasing capital economies of scale and rising fuel transportation costs. The optimum size of power plant based on whole forest, forest harvest residues and agricultural residues are 900 MW, 137 MW and 450 MW respectively. Power costs estimated for the three fuels were $72 per MWh, $96 per MWh and $76 per MWh respectively. Power cost is highest for forest harvest residues because of the large dispersed area of the fuel that results in high fuel transportation cost. One striking feature of biomass power for whole forest and agricultural residues is the minor change in power cost from 200 MW to 3000 MW, resulting in a low capital cost penalty for building smaller size plants down to 200 MW. The greenhouse gas (GHG) credit that would have been required to make biomass power competitive over the last three years (based on monthly average power pool price in Alberta) ranges from $0 per tonne of CO 2 to $71 per tonne of CO 2. Introduction Global warming caused by the buildup of carbon in the atmosphere from fossil fuel usage is a critical issue. Three main ways of mitigating the impact of fossil fuel GHG are conservation, sequestration and substitution of carbon neutral fuels for fossil fuels in current or future developments. Stationary power generation is an ideal application for replacement of fossil fuel. Alberta has the largest hydrocarbon base in North America. Canada and Alberta s economic future depends in part on how effectively they deal with GHG mitigation issues. In addition to its large fossil fuel resource base, still essential for transportation fuels, Alberta has two other factors that make it a unique location to explore biomass fuels: it has large resources of biomass, both forest and agricultural, and it has a growing power demand, as evidence by two active projects to develop additional coal based power generation. One alternative for Alberta to meet its future power needs is the development of biomass based power generation. Biomass is effectively carbon neutral as the combustion of biomass produces essentially the same amount of carbon dioxide as is taken up by plants as they regrow. This study was undertaken to evaluate the basic economics of generating power from biomass. The study considers three biomass fuel sources: whole forest biomass (trees 1

2 from the forest, cut whole and chipped), chipped logging residues (the branches and tops of trees that today are left on the roadside after pulp and lumber operations), and wheat and barley straw from the black soil region of central Alberta. We determine the optimum size and power cost at optimum size of biomass power plants based on the three biomass fuels. We also determine the amount of carbon credit, in dollars per tonne of CO 2, that would be required to make each biomass fuel competitive at historical power prices in Alberta. Each biomass source warrants some further comments. Use of the whole forest as a fuel precludes its usage as fiber in either lumber or pulp; hence there is a foregone royalty to the Province (stumpage) and foregone economic activity. This would only make sense for Alberta if the royalty value from fossil fuel development required offsetting carbon credits and if the hydrocarbon royalty at risk were far greater than the offsetting timber royalty. This tradeoff is the subject of a future study. Forest harvest residues are in essence freely available: they accumulate at roadside in current timber cutting operations, and must be disposed of by burning to avoid a forest fire hazard. Hence, if collected and burned to generate power, a useful product is obtained from a material that is already combusted, and the use of fossil fuels to generate incremental power could be avoided. Some straw in the Province is collected for animal bedding or in rare cases animal feed, but most is left on the field to rot. Previous studies have demonstrated that collection of straw from black soils does not reduce soil carbon; presumably the carbon in roots and the residual short stalks is enough to sustain soil carbon. Finally, we have not evaluated power generation from mill residues such as sawdust and bark, since over half is already being used, and the remainder is likely under development given recent high natural gas prices. Biomass resources in Alberta Northern Alberta is covered with boreal forests, consisting mainly of conifers and hardwoods (mostly species of poplar). This study is based on a typical blended forest of spruce and hardwoods. The average biomass yield was estimated to be 84 dry tonnes of biomass per hectare [1]. In the whole forest case, trees would be cut and skidded to the roadside, as is currently done in lumber and pulp operations. However, at the roadside whole trees would be chipped and the chips would be transported to the biomass power plant by dedicated chip van trucks carrying 36 tonnes of chips in two trailers. Existing forest harvesting produces long windrows of residues; the residues range from 15 to 25% of the total biomass in the harvested trees. Note, however, that harvesting of existing timber management areas is dictated by a number of ecological and forest management considerations, and hence is scattered over a wide area. Rotational periods are typically 80 years for hardwoods and as much as 120 years for spruce. Hence, forest harvest residues are widely dispersed. In this study, we assume an average rotation of 100 years, and the resulting yield of forest harvest residues per total area of forest is dry tonnes per gross hectare. 2

3 Straw yield per total area (including developed land not used for agriculture or used for non-grain crops) was estimated based on detailed records of grain production in black soil areas of Alberta. In this study we used an average straw production density of tonnes of dry straw per gross hectare in an agricultural district [2]. A moisture level of 16% is assumed for straw, 50% for wood chips from the whole forest, and 45% for wood chips from forest harvest residues because the residues would sit for a while at roadside before being chipped. Straw hence has a higher lower heating value (LHV) than wood. Power cost and optimum size of a biomass power plant using direct combustion technology Biomass has been widely used around the world for power generation, although rarely in facilities that were based purely on commercial economic analysis; many units are demonstration units or have economics dictated by the alternate disposal cost of wastes. In North America there are over 500 biomass based plants, mostly wood based, and in Europe there are several straw burning plants that produce heat or heat plus power. The cost of power from a biomass facility is highly dependent on size. The optimum size of a biomass power plant is a trade-off between the transportation cost of biomass that rises with increasing plant capacity (since the collection area for biomass increases), and the unit capital cost that decreases with increasing plant capacity, due to economies of scale in construction and operation of power plants. As a result of these conflicting cost elements, there is a particular capacity where power cost is at a minimum and the plant is at its optimum size. In this study, all costs have been estimated based on application of existing technologies and practices. Harvesting costs for biomass are based on current forestry and farming practice, and transportation costs are in turn based on current costs of truck transport. The maximum size of a single boiler burning biomass was set at 450 MW with an efficiency of 34% (power output over LHV input). Unit size is comparable to coal fired units currently under development in Alberta. The assumption of maximum boiler size is a critical assumption, because up to that size unit capital costs incorporate a scale factor (0.75 was used in this study), while above that size the cost of a second or higher unit identical to a first unit is assumed, based on discussions with engineering and construction firms, to be 95% of the cost of the original unit. All cost factors have been included in the study. Acquisition of biomass from the owner includes both an acquisition payment of $6 per dry tonne of biomass and a payment for all direct costs including labor and capital recovery (for instance, a farmer delivering straw to roadside would be paid for time, equipment, and the replacement value of nutrients plus a unit payment of $6 per dry tonne of biomass; the resulting value of straw is well above current market value). Ash disposal is treated as a cost, although there is some evidence that over time ash will be removed by farmers at zero cost and spread by them to recover the nutrient value, mainly potassium and phosphate. Both the straw and 3

4 forest harvest residue plants are assumed to be located in existing towns adjacent to transmission, but the whole forest case is assumed to be remotely located, and costs are included for higher construction and operation cost of a remote facility plus a dedicated transmission line, including line losses. In the case of harvesting the whole forest, costs for road construction are included, whereas in the case of straw and forest harvest residue the biomass is transported over existing roads. The whole forest case also includes silviculture (replanting) costs, while for the forest harvest residue case these costs would be charged to the lumber or pulp operation, as at present. For straw, as noted above, nutrient replacement cost for the nitrogen, phosphorus and potassium removed with the straw is included as a cost, although we assume no incremental cost for spreading as the farmer is already making a fertilizing pass over the crop in the spring, and only the dosage would increase if straw were harvested. In the case of whole forest and forest harvest residues, nutrient replacement is not factored in to costs as current practice is not to replace nutrients after the first cut. Ultimately repeated harvesting of the forest would require nutrient replacement, but this is not scheduled to occur in the next 60 years. Capital recovery is based on an assumed 10% return on equity associated with a rate based power generation plant. Costs are discussed in detail in Kumar et al. [3]. Table 1 shows the cost of biomass power at the optimum size for the three fuels. The size of the whole forest biomass based power plant is 900 MW (two maximum sized units), and the optimum size for straw is 450 MW (one maximum sized unit). The high transportation cost for forest harvest residues gives a smaller optimum plant size, 137 MW. Table 1 also shows the area over which fuel collection would be done over the life of the plant (assumed to be 30 years in this study). The collection area for forest residues is the largest because of the low yield per hectare. Table 1: Economics optimum size of biomass power plant in Alberta Biomass source Biomass yield (dry tonnes per gross hectare) Optimum size (MW) Project area from which biomass is drawn (km 2 ) Agricultural residues Whole forest Power price ($/MWh) , , biomass Forest residues , Source: [3, 4] Figure 1 shows the cost of biomass power at different capacities of the biomass power plants. For forest harvest residues there is a sharp optimum, but in the case of agricultural residues and the whole forest biomass the optimum size is a wide range, i.e. the power cost curves for agricultural residue and whole forest biomass are flat. This suggests that for these fuels, the capital cost penalty would be low for building smaller size power plant. For the whole forest case the cost of power is nearly the same for a range of 200 MW to 2500 MW. This flat profile is different from the fossil fuel based power plants where larger size gives a lower power cost. Hence, although the optimum size of a biomass power plant using the whole forest or straw is larger, the likely size of an initial 4

5 plant would be in the 200 MW range because the cost penalty for this smaller size is minimal. Plant Size vs Power Price 160 Power Price (year 2000 Cnd $ / MWh) Whole Forest Forest Residues Straw Figure 1: Power cost as a function of capacity for three biomass fuels, Source: [3, 4] Table 2 shows the different cost components of the biomass power cost. It is evident that power from biomass fuel is not economic today. Road construction and silviculture are significant cost factors in the whole forest case, as is dedicated transmission; none of these costs occur for the other two cases. However, straw harvesting requires nutrient replacement, which is a significant cost in this case only. The main penalty incurred with forest harvest residues is the high transportation cost that is caused by the highly dispersed nature of the fuel. Power cost for biomass gasification Plant Size (MW) The cost of biomass power and optimum plant size was also evaluated for biomass integrated gasification and combustion of the produced gas in a combined cycle turbine (BIGCC). A unit size of 130 MW was assumed, based on the largest known unit. The specific technology selected was a pressurized fluidized bed integrated combined cycle. The overall efficiency of power generation was assumed to be 39.7%. These assumptions draw on the work of Craig and Mann [5]. Table 3 shows the cost of biomass power cost and optimum size for biomass gasification. In the case of forest harvest residues, power cost decreases because the saving arising from the increase in the efficiency of the plant is more dominant than the increase in the capital cost. For whole forest and agricultural residues the result is the opposite, i.e. the increment in capital cost is more dominant than the saving from the increased efficiency of the plant, and the result is a higher power 5

6 price for gasification compared to the direct combustion case. Figure 2 shows the percentage change in the power price in case of biomass gasification as compared to direct combustion. The power price for whole forest and agricultural residues increases by 13% and 2.3% respectively while for forest harvest residues it decreases by 7% at their optimum size. Table 2: Cost of power from biomass using direct combustion technology, year 2000 Canadian $ MWh -1, at full capacity (year 3) and optimum size Cost element Whole forest Forest harvest Agricultural residue residue Capital Recovery Transportation Harvesting Maintenance Operating Administration Field Cost of Biomass Silviculture Road Construction Nutrient Replacement Transmission Ash disposal Total Source: [3, 4] Table 3: Power cost and optimum size for a biomass integrated gasification combined cycle power plant Biomass fuel Optimum size of the power plant (MW) Power cost at the optimum size ($/MWh) Whole forest Forest harvest residues Agricultural residues Source: [6] The primary factor in these different results is the delivered cost of fuel. Gasification, which spends capital dollars to improve efficiency, is beneficial for fuels which have high delivered cost, but is detrimental for low cost fuel. The results are specific both to the delivered cost of biomass fuel and the capital cost increment for gasification. While the cost of power from forest harvest residues is reduced by gasification, the impact is not large enough to make it competitive with direct combustion of whole forest or agricultural residues. 6

7 Effect of Biomass Gasification on Power Price Percentage Change in Power Price Whole Forest +13 % Agricultural Residues +2.3 % Delivered Cost of Fuel ($/MWh) Forest Harvest Residues -7 % Figure 2: Effect of biomass gasification on power price Estimated cost of greenhouse gas credits for power from direct combustion of biomass in Alberta GHG credits would be required to develop biomass power in Alberta, as none of biomass-based power is competitive with coal. Figure 3 shows the GHG credits that would be required to make biomass power economic in Alberta as a function of power price. These values can be used to calculate a variable incentive required to sustain a biomass power plant. Power Cost ($ / MWh) Cost of Power Cost vs. Carbon Credit Whole Forest Wood Residues Straw Carbon Credit ($ / tonne CO2) Figure 3: Power cost versus carbon credit required for biomass power. At an average monthly power pool price of $45 per MWh in Alberta, GHG credits required to make the biomass power competitive for the whole forest, the forest harvest 7

8 residues and the agricultural residues would be $25 per tonne of CO 2, $45 per tonne of CO 2 and $29 per tonne of CO 2 respectively. Note that these values are high compared to cap on carbon credits announced by the Federal government of Canada of $15 per tonne of CO 2. The same figures for $60 average pool price of power are $11, $32, and $15 respectively. The average monthly power pool price in Alberta has varied from $27 per MWh to about $260 per MWh over last three years. Figures 4, 5 and 6 show the greenhouse gas credits that would have been required to make the biomass power competitive in Alberta Carbon credits required ($/tonne of CO2) Jan-00 Mar-00 May-00 Jul-00 Sep-00 Nov-00 Jan-01 Mar-01 May-01 Jul-01 Sep-01 Nov-01 Jan-02 Mar-02 May-02 Jul-02 Sep-02 Nov-02 Jan Months Figure 4: Carbon credits that would have been required for whole forest based power to be competitive While the net credit over the 38 month period shown in Figures 4 through 6 are negative, this likely reflects an unusual period of high power prices that arose with the long delays in development of new power generation during the initial uncertainty prior to the onset of deregulation of power price in Alberta. A power price of $45 to $60 is a more reasonable planning basis for evaluating the potential support required through carbon credits for biomass power in Alberta. Issues in making biomass power possible The prospect of biomass power raises some policy issues that will have an impact on the rate at which it develops: 8

9 Carbon credits required ($/tonne of CO2) Jan Mar-00 May-00 Jul-00 Sep-00 Nov-00 Jan-01 Mar-01 May-01 Jul-01 Sep-01 Nov-01 Jan-02 Mar-02 May-02 Jul-02 Sep-02 Nov-02 Jan Months Figure 5: Carbon credits that would have been required for forest harvest residues based power to be competitive Carbon credits required ($/tonne of CO2) Jan-00 Mar-00 May-00 Jul-00 Sep-00 Nov-00 Jan-01 Mar-01 May-01 Jul-01 Sep-01 Nov-01 Jan-02 Mar-02 May-02 Jul-02 Sep-02 Nov-02 Jan-03 Months Figure 6: Carbon credits that would have been required for agricultural residues based power to be competitive 9

10 Security of fuel supply: Because of the large capital investment required to build a power plant, security of fuel supply is a critical factor in developing any new power project. Biomass power, particularly a project that uses agricultural residues, raises important questions about how to secure a long term fuel supply, and government can, if it chooses, play a role. For forest harvest residues the government could tie timber rights to an obligation on forest companies to make the forest residues available at the roadside. This would not likely meet high resistance since currently disposal of residues by burning is a net cost to forestry companies. For forest harvest residues, the payment of $6 per dry tonne included in this study could possibly be avoided. For the whole forest, it is the Government of Alberta that acts as owner, and it could presumably grant long term timber cutting rights for this end use. Securing a supply of straw is more problematic, because of the diverse ownership of straw in the field. The government could tie farm subsidies to a requirement that the farmer make straw available for power generation at a cost, i.e. in effect the government could act as a buyer of straw in lieu of other farm subsidies. This kind of market intervention would require careful analysis. Should the government provide a regulated rate of return? The biomass power plant would be a new concept for the Alberta power developers, and its benefit would in part flow to the Province of Alberta as the primary owner of the hydrocarbon resource. One can also expect that the cost of constructing a first biomass power plant in western Canada would be higher than for subsequent plants. One option the government could explore to accelerate GHG mitigation through biomass power is to revert to a rate based (regulated) rate of return for biomass based power. Given the recent history of deregulation of electrical power in the province, this would be a significant policy decision. GHG credits tied to Alberta price market: Figures 4 through 6 demonstrate that the carbon credit necessary to support biomass power varies sharply with power price. At times of high power price, the GHG credit is actually negative, reducing the net long term cost of the credit. The government could relate the GHG credit to the market price of power under a rate based scheme, and could also do so through the structure of a specific market for carbon credits from biomass power. Conclusions Power can be generated from direct combustion of biomass from the whole forest, from forest harvest residues, and from agricultural residues (wheat and barley straw) in Alberta for $72, $96 and $76 per MWh. Fuel cost is the reason for the difference in cost; transportation of fuel to the plant site is the most significant cost factor that varies between the three cases. The optimum plant size associated with these costs is 900, 137 and 450 MW respectively. For forest harvest residues, the optimum plant size is a sharp minimum, and power cost increases significantly at smaller or larger plant sizes. For whole forest and agricultural residues, costs are quite flat for a wide range of plant sizes, and plants as small as 200 MW could be built with similar overall power cost. 10

11 Gasification instead of direct combustion lowers the cost of power from forest harvest residues, to $89 per MWh, but increases the cost of power from the whole forest and agricultural residues. Gasification has a higher capital cost and higher efficiency; the incremental spending is only justified for biomass fuels with a high delivered cost. Greenhouse gas (carbon) credits would be necessary to make biomass based power competitive in Alberta. Alberta s large biomass resource base, large fossil fuel reserve that will likely require carbon credits to be developed, and growing power demand make it an ideal location to explore biomass based power. The greenhouse gas credit required to sustain biomass power varies with power price in Alberta. In the range of $45 to $60 per MWh power, the carbon credit required to support power generation from either the whole forest or from straw ranges from $11 to $29 per tonne of CO 2. References 1. Alberta Energy and Natural Resources. Alberta Phase 3 Forest Inventory: Yield Tables for Unmanaged Stands, Carcajou Research Limited. Alberta annual report on small areas Kumar A., Cameron J.B., and Flynn P.C., Biomass Power Cost and Optimum Plant Size in Western Canada, accepted for publication in Biomass and Bioenergy, 2002, Vol. 24(6), pp Kumar A., Cameron J.B., and Flynn P.C., Optimum Biomass Power Plant Size in Western Canada, presented at The Tenth Biennial Bioenergy Conference, BIOENERGY 2002, Sept , 2002, Boise, Idaho, USA. 5. Craig KR and Mann MK. Cost and performance analysis of three integrated biomass gasification combined cycle power systems. NREL, Golden, CO, See: library/index.htm 6. Cameron J.B., Kumar A., and Flynn P.C., Optimizing Technology for Biomass for Power Generation, presented at The 12 th European Conference and Technology Exhibition on Biomass for Energy, Industry and Climate Protection, June