**4. Conclusions**

The available amount of biomass including forest and agriculture residues reached 41.84 million tons in 2016. However, biomass resources with uneven distribution have a gradually decreasing trend from north to south. The distribution of the power plants is not consistent with the biomass potential, especially in the central and southern areas. The biomass density also indicated that these areas may not be suitable for biomass power plant development due to the higher operational cost for feedstock transport. However, the biomass power plants showed great potential for GHG emissions mitigation with a value of 3.44 million tons CO2-eq in 2016. However, further research, especially more quantitative synthetical analysis, should be conducted to quantify the impacts of straw-based biomass power plant in China.

**Author Contributions:** H.L. and X.M. conceived and designed this case-study as well as wrote the paper; M.D. and X.D. reviewed the paper; all authors interpreted the data. H.L. and X.M. authors contributed equally to this work as co-first authors.

**Funding:** This work was financially supported by the Youth development project from School of Resources and Environment AHAU, the Project Startup Foundation for Advanced Talents AHAU (No. YJ2018–56), The Natural Science Foundation of the Education Department of Anhui Province (NO. KJ2019A0207). The authors would like to thank the anonymous reviewers for their helpful comments, which improved the content of the present article.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **Appendix A**

#### *Appendix A.1 Statistical Methods for Biomass Resources*

The amount of biomass resources in a region can directly determine whether the area is suitable for the development of biomass power generation. The crop straw and agro-forestry biomass resources were used as the main parts to calculate the biomass resources of the power industry in a region, and the two methods used to calculate these resources are as follows:

#### Appendix A.1.1 Crop Straw Resources

Crop straw, which refers to the stalk or stem of certain grains produced in the field, mainly includes rice straw, wheat straw, cotton straw, maize straw, bean straw and potato straw in AHP. The collectable amount of crop straw can be expressed as follows:

$$A\_{\mathcal{Y}} = \left(\sum\_{j} F\_{jy} \times \text{CRI}\_{j}\right) \times \eta\_{jy}$$

$$\eta\_{jy} = (\text{RM}\_{jy} \times \text{IM}\_{j} + \text{RP}\_{jy} \times \text{IP}\_{j}) \times (1 - I\_{\text{loss}})$$

where *Ay* refers to the total collectable amount of straw in year *y*, *Fjy* is the yield of crop *j* in a year *y*, *CRIj* refers to the residue/grain ratio of crop *j* (Table A1), η*jy* refers to the collection coefficient of crop *j* in year *y*, *RMjy* is the mechanized harvesting ratio of crop *j* in year *y*, RPjy is the manual harvesting ratio of crop *j* in year *y*, *IMj* and *IPj* are the respective machinery and manpower harvesting straw coefficients of crop *j*, and *Iloss* refers to the loss rate of straw in the harvest process, which was 0.05 in this study. Crop yield data in this paper were derived from the Statistics Bureau of AHP.

**Table A1.** Crop residue/grain ration and collect index in AHP.


Note: Residue/grain ratio data were obtained from the "Comprehensive utilization planning of crop straw", issued by the National Development and Reform Commission Office and the Ministry of Agriculture.

#### Appendix A.1.2 Forestry Byproducts

Forestry byproduct resources refer to tree trunks, branches and leaves that remain from the process of harvesting and wood processing. This paper estimates the amount of forestry byproduct resources by taking the wood and bamboo harvesting quantity as the main parameter.

The calculation used to determine the amount of agro-forestry biomass resources in AHP is as follows:

where F: Amount of agroforestry biomass resources (104 t)


The details of the calculation method are as follows:

*Processes* **2019**, *7*, 608

Amount of Residue from Wood Harvesting

$$\mathbf{F}11 = \mathbf{V} \times \mathbf{b} \times \left[ (1 - \mathbf{r}\_1) / \mathbf{r}\_1 \right]^2$$

Amount of Residue from Wood Production and Processing

$$\text{F12} = \text{V}\_1 \times \text{pr} \times \text{rr}$$

Amount of Residue from Bamboo Harvesting

$$\mathbf{F13 = A \times g \times r\_2}$$

Amount of Residue from Bamboo Production and Processing

$$\mathbf{F14 = A \times g \times r\_3}$$

The amount of agroforestry biomass resources and associated parameters obtained from other studies are listed as follows:


*Appendix A.2 The Calculation Method of GHG Emissions Reductions of Biomass Power Plants According to Clean Development Mechanism (CDM)*

The greenhouse gas emission reduction of biomass power plant can be described by the following equation of CM-092-V01:

$$\text{ER}\_{\text{Y}} = \text{BE}\_{\text{Y}} - \text{PE}\_{\text{Y}} - \text{LE}\_{\text{Y}}$$

where ERy refers to the emissions reductions of the project activity during year y (t CO2), BEy is defined as the base line emissions during year y (t CO2), PEy is the project emissions during year y (t CO2), and LEy denotes the leakage emissions during year y (t CO2).

Appendix A.2.1 Baseline Emissions

$$\text{BE}\_{\text{Y}} = \text{BE}\_{\text{EL},\text{Y}} + \text{BE}\_{\text{BR},\text{Y}}$$

where BEy refers to the baseline emissions during year y (t CO2); BEEL,y refers to the baseline emissions due to generation of electricity in year y (t CO2); BEBR,y is the baseline emissions due to uncontrolled burning or decay of biomass residues in year y(t CO2).

Baseline Emissions from Electricity Generation

$$\text{BE}\_{\text{EL},\text{y}} = \text{EG}\_{\text{PL},\text{y}} \times \text{EF}\_{\text{BL},\text{HL},\text{y}}$$

where BEEL,y refers to the baseline emissions due to generation of electricity in year y (t CO2); EGPJ,y is defined as the net quantity of electricity generated in the power plant in year y (MWh); EFBL,EL,y is the emission factor for electricity generation in the baseline in year y (t CO2/MWh).

The Calculation of Uncontrolled Burning or Decay of Biomass Residues BEBR,y

$$\text{BE}\_{\text{BR},\text{y}} = \text{BE}\_{\text{BR},\text{B1}/\text{B3},\text{y}} + \text{BE}\_{\text{BR},\text{B2},\text{y}}$$

where BEBR,y is the baseline emissions due to uncontrolled burning or decay of biomass residues in year y(t CO2); BEBR,B1/B3,y refers to the Baseline emissions due to aerobic decay or uncontrolled burning of biomass residues in year y(t CO2); BEBR,B2,y is the baseline emissions due to anaerobic decay of biomass residues in year y (t CO2).

Appendix A.2.2 Project Emission

$$\text{PE}\_{\text{Y}} = \text{PE}\_{\text{FF,Y}} + \text{PE}\_{\text{EL,Y}} + \text{PE}\_{\text{TR,Y}} + \text{PE}\_{\text{BR},\text{y}} + \text{PE}\_{\text{W}\text{V}\text{W},\text{yr}}$$

where PEy is defined as the project emissions during year y (t CO2); PEFF,y denotes the consumption (t CO2) is the emissions during the year y due to fossil fuel; PEEL,y refers to the emissions during the year y due to electricity use off-site for the procession of biomass residues(t CO2); PETR,y refers to the emissions during the year y due to transport of the biomass residues to the project plant(t CO2); PEBR,y refers to the emissions from the combustion of biomass residues during the year y(t CO2); PEWW,y refers to the emissions from wastewater generated from the treatment of biomass residues in year y(t CO2).

Appendix A.2.3 Leakage Emissions

$$\rm LE\_Y = EF\_{CO2,LE} \times \sum\_{n} \rm BR\_{PJ,n,y} \times \rm NCV\_{n,y}$$

where LEy is defined as the leakage emissions during year y (t CO2), EFCO2,LE refers to the CO2 emission factor for fossil fuels with the highest carbon content in China(t CO2/GJ); BRPJ, n, y is the amount of biomass waste of category n used by the project plant within the project boundary in year y (GJ/dry basis t); NCVn,y is the net calorific value of biomass waste of category n in year y(GJ/dry basis t).

#### **References**


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