*3.1. Biomass Production and Characterization*

Biomass resource potential is an important challenge for the development of biomass power plants. AHP has a huge amount of biomass resources from agriculture and forestry. The total land area is 139,427 km2, of which 58,730 km2 is cultivated land and 39,585 km2 is forest land [35]. Production of crop straw is evaluated based on the crop-to-residue index (CRI) value, namely 1.38 for wheat straw, 2.05 for corn straw, 1.26 for rice straw, 1.68 for bean straw, and 1.16 for potato straw [36].

Biomass availability in AHP varied in term of spatial and temporal distribution. Figure 3 shows the availability of total biomass production from 2012 to 2016. The total yield increased slowly from 36.25 to 41.84 million tons, with the highest value of 43.20 million tons in 2015. The forestry byproducts gradually increased at a rate of 23.15% due to the increase in forest area supported by the local government. The crop straw yield was raised to 36.41 million tons in 2016, with an increased rate of 4.52%. Our previous research indicated that the total crop production and harvesting approach are the two main factors that impact straw production, and with the rapid development of mechanized harvesting, less straw is collected for utilization [36].

**Figure 3.** The total collectable amount of biomass resource in Anhui Province (AHP) from 2012 to 2016.

Abbreviation of cities: SZ for Suzhou city, BZ for Bozhou city, FY for Fuyang city, BB for Bengbu city, HN for Huainan city, XC for Xuancheng city, HB for Huaibei city, HF for Hefei city, LA for Lu'an city, Cuz for Chuzhou city, MAS for Ma'anshan city, WH for Wuhu city, TL for Tonglin city, CiZ for Chizhou city, AQ for Anqing city, HS for Huangshan city.

Geographically, biomass availability is spatially nonuniform in AHP and is disproportionately concentrated in the northern part of AHP as showed in Figure 4, because of the different land availability and productivity. The total biomass production was mainly concentrated in the northern part of AHP, with a proportion of 56%, compared with 22.3% and 21.7% in central and southern AHP, respectively. With respect to forestry byproducts, approximately 63.57% of the resources were generated from the southern part of AHP, such as Xuancheng, Chizhou, Huangshan cities. In addition, the distribution of the biomass power plants is not consistent with that of straw resources, except for Huangshan and Tongling cities, which have no power plant due to their low biomass availability. However, installed capacity of Lu'an city was the highest among all the cities, although the biomass availability is low.

**Figure 4.** The biomass availability and installed capacity of biomass power plant in AHP, 2016.

#### *3.2. Assessment and Availability Analysis*

The high production of biomass in AHP provides opportunities for the development of biomass power plants. The Chinese official legislation promulgated in 2006 restricted the outdoor burning of straw, and approximately 23.7% of straw is used for fuel. Biomass availability is dependent largely on location and climate. To better describe the distribution of biomass, it is common to select the biomass density, which is defined as the ratio of the collectable biomass production to the total land area [37]. It is concluded from previous studies that a low biomass density will result in high collection, delivery and storage costs. As showed in Figure 5, the density of biomass resources for each city was calculated. It should be noted that the geographical straw density differed considerably from 75.40 to 733.30 t/km2, with a mean value of 361.77 t/km2. However, the biomass density decreases gradually from north to south in AHP which is consistent with the results found in other literature [36]. Bozhou and Fuyang have high densities, more than 700 t/km2, and the densities of central and southern AHP (Hefei, Wuhu, Maanshan, Lu'an, Tongling, Xuancheng, Chizhou, Anqing, and Huangshan) are relatively low, less than 300 t/km2, and the lowest value is observed in the southern area.

**Figure 5.** The biomass density in AHP (unit: t/Km2).

With low-density energy resource, the distribution and sustainable supply of biomass feedstock have a great influence on the collection and storage cost [38]. It is recommended that the economical collection radius should be less than 50 km for profitability [30]. In addition, only 20% of the available biomass is used for power plants in general due to their alternative utilization activities. Therefore, the net theoretical available potential (NAP, within a 50 km radius with a supply assurance factor of 0.3) amount of biomass for power generation was calculated in this study. The biomass consumption was approximately 0.17–0.29 million tons for a 30 MW biomass power plant based on the calorific values [39]. As shown in Figure 6, within 50 km, the biomass from northern AHP can completely fuel the demand of a power plant, while the central and southern AHP exhibited a lower NAP, making it difficult to meet the feedstock demand. Most biomass power plants have a relatively low capacity for biomass collection, leading to the final price of biomass reaching more than approximately 50 USD per ton, which is economically unacceptable.

**Figure 6.** The maximum net theoretical available potential (NAP) of biomass in each city from AHP (with the supply assurance factor of 0.3).

#### *3.3. General Status of Biomass-Based Power Generation*

The first 2 × 15 MW biomass-based power plant in AHP was established in 2006, with a total investment of 280 million RMB by the Datang Power Group in Anqing City. According to statistics, this project consumes 235,000 tons of biomass and generates more than 190 GWh of electricity per year. A total of 20 grid-connected biomass power plants with a power capacity of 6560 MW have been installed by the end of 2016 such that AHP possess the second largest biomass capacity in China. The power plants in AHP are in the range of 24–30 MW with an average scale of 28.5 MW, which is much smaller than that of coal-fired power plants. A total of 73.9% of the plants are designed for 30 MW due to the limit of fuel sources, capital and operational costs, and other factors [40].

According to the statistical data from the Anhui Energy Bureau, the total power generation of 20 biomass power plants in 2016 was 377.1 billion KWh, with a total operation of 132,980 h in 2016. As shown in Figure 7, the annual utilization hours of the 20 straw-based power plants varied greatly from 3275 to 8184 h, with a mean value of 6649 h. Nearly half of the plants operated for more than 6000 h per year. The power generation varied between the 20 plants, the highest was 244.45 million KWh in Suzhou City, and the lowest was 98.27 million KWh in Lu'an City.

Compared with fossil energy, there is generally no economically competitive biomass energy due to its high capital, operating and maintenance costs [41,42]. The investment cost of biomass power plants is relatively higher than that of thermal power and hydropower plants, even though the cost has decreased in recent years. Based on the estimation by Zhang et al. [32], the average unit cost is approximated 9900 RMB/kW or 0.738 RMB/KWh, more than double of that of a thermal power plant [43]. In addition, the high cost of handling and shipping is still challenging for some biomass power plants in AHP, especially with the shortage of rural manpower [38]. The biomass purchased price should be less than 220 RMB/ton to provide a benefit.

**Figure 7.** The annual operation hours and power generation of biomass based power plant in AHP, 2016.

Due to the relatively high investment and operating costs of biomass based power plants, various auxiliary policies such as financing policies, tax policies, mandatory grid connection and price support (feed-in tariff) have been proposed [32,44]. The "Renewable Energy Law" announced in 2005 and modified in 2009 indicated that favorable tariffs, development funds, and fiscal support were adopted for renewable energy development. The feed-in tariff set for agricultural and forestry residual power plants was 0.75 RMB/KWh from 2010, of which 0.35 and 0.40 RMB was supported by government subsidies and national grids, respectively. However, the costs of fuel supplies still take a large share in the operational costs, with 60–70% of the total cost [30]. Zhang et al. [32] noted that most biomass power plants in China were operating at a loss even under the support of polices in 2012. Except for the national support funds, the first financial subsidies for straw utilization were issued by the Anhui government in 2014, i.e., 50, 40, 30 RMB/tons for rice, wheat and other straw collections, respectively [45]. Under these subsidies, the number of straw collections was increased, resulting in the 17 out of 20 power plants making profits in 2016, based on the statistics from the Anhui Energy Bureau.

#### *3.4. GHG Emissions Mitigation Analysis*

Compared with fossil fuels such as coal, natural gas, and oil, a biomass power plant may effectively reduce greenhouse gas emissions and relieve the pressure of global climate change [46,47]. A study conducted by Sanchez et al. [20] estimated that the CO2 capture and sequestration potential of biomass for electricity is two times higher than that of biomass for cellulosic ethanol. The direct combustion of biomass for electricity generation is an appropriate approach for GHG mitigation, according to the investigation of Stefan Muench [48]. Based on the CM-092-V01 method of the Clean Development Mechanism (CDM) derived from the database of the United Nations Framework Convention on Climate Change (UNFCCC) and the Intergovernmental Panel on Climate Change (IPCC), the greenhouse gas emission reduction attributed to biomass power plants in AHP was calculated and is shown in Table 1. The GHG mitigation attributed to biomass power plants in AHP ranged from 41,217 to 311,148 t CO2-eq, with a total yield of 3,436,490 t CO2-eq in 2016. The different emissions reduction values are caused by equipment and depend on the scale of the plant, the raw material supply, the biomass

utilization technology, target products and so on [49]. The reductions per unit production of a biomass power plant differ considerably aiming the power plants, ranging from 0.58 to 1.32 with a mean value of 0.75, which is comparable to the data reported by Lin and He [43].


**Table 1.** Emission reductions of biomass power plants in 2016.
