Comparative Evaluation of Biomass Power Generation Systems in China Using Hybrid Life Cycle Inventory Analysis

Table 9

Major parameters for biomass power plant.

Items	25 MW biomass-only; fired	140 MW; cofiring	25 MW; cofiring	1 MW; gasification	5.5 MW; gasification
Electric efficiency^a	25.6%	35.4%	27.6%	18.0%	27.0%
Electric efficiency before cofiring		36.1%	28.0%
Cofiring ratio by energy		20%	15%
Auxiliary power consumption rate^b	8%	10%	8%	10%	10%
Annual operating hours (h)	6500	7000	7000	6000	6000
Annual power supply^c (GJ)	538200	571536	78246	19440	106920
Life expectancy (year)	15	10	10	15	15
Capital investment (10^4 yuan)^d	24145	8413	1155	428	3350
Annual cost (10^4 yuan)^e	3255	1148	230	92	572
CH4 emission^f  (kg/GJ biomass)	0.0037	0.0037	0.0037	0.0037	0.0037
N2O emission^f  (kg/GJ biomass)	0.0105	0.0105	0.0105	0.0105	0.0105
SO2 emission^g  (kg/GJ biomass)	0.2393	0.0299	0.0299	0.0008	0.0008
NO emission^h  (kg/GJ biomass)	0.0590	0.3291	0.3300	0.1733	0.1733

^aUtility boiler efficiency decrease: 1% for each 10% of coal replaced by biomass (on an energy basis) [2].
^bEnergy consumption of biomass crushing is included.
^cThe energy inputs of the boiler in cofiring plant remain the same as before. The biomass-related power output was listed as the annual power supply of cofiring plant.
^dInvestment on feedstock supply system is not included.
^eThe annual cost consists of depreciation cost, maintenance, materials, and personnel. The cost of feedstock supply is not included.
^fSince all the carbon in the biomass is recycled, it has been assumed that biomass fuel combustion does not produce GHG emissions due to CO₂. The CH₄ and N₂O emission factors of biomass-only fired plant and biomass gasification system were taken from Wang [25]. In addition, the CH₄ and N₂O emission of internal engine is assumed to be the same as that of IGCC from Wang [25]. As in the cofiring case, the emission factors of CH₄ and N₂O were assumed to be the same as that of biomass-only fired system.
^gFor biomass gasification power plant, the SO₂ emission may vary significantly from one to another. The data of the 5.5 MW gasification system adopted here is converted from Jia [29]. And the 1 MW gasification system is assumed to have the same emission. Desulphurization device is not usually commissioned in a biomass-only fired plant, since sulfur content of biomass is usually low. The SO₂ emission of biomass-only fired plant is estimated to be 80% of that of feedstock. On the other hand, the SO₂ emission factor of cofiring plant is estimated to be 10%, for desulphurization is commonly used. The sulfur content of coal in the cofiring case is 1.29 wt% [16].
^hThe NO emission factor of biomass-only fired plant was converted from Liu et al. [8]. For biomass gasification power plant, the NO emission is converted from Jia [29]. And the 1 MW gasification system is assumed to have the same NO emission factor. NO emissions reduction can be achieved by cofiring and is calculated using an equation from Tillman [30], which can be expressed as RNO = 0.0008² + 0.0006 + 0.075, where is the percentage biomass cofiring on a calorific basis. The NO emission factor of coal before cofiring is 335.94 g/GJ coal [16].