Comprehensive evaluation of the utilization system of crops straw in China:
A case study of Heilongjiang Province
University of Tsukuba

Jin Xuemei*

University of Tsukuba

Helmut Yabar,

University of Tsukuba

Mizunoya Takeshi,

University of Tsukuba

Higano Yoshiro

1. Introduction
With the development of economy and energy crisis, people are searching for new substitutive energy [1]. China is a large
agricultural country whose annual crop yield is more than 700 million tons of which straw is 399.5 million tons[2].Heilongjiang province is a large province of energy consumption. The restriction of traditional fossil fuel and theenvironmental burden brought by it is now hindering the sustainable development of Heilongjiang Province[3]. Large yield ofstraw in Heilongjiang Province provides a promising condition for the utilization of this kind of renewable energy [4].
2. Reserve evaluation of straw in Heilongjiang Province
Straw mainly comes from food crops, oil crops, soybean, tubers and hemp. Besides reused to field, industrial raw materials
and fodders, straw can be used as energy [5]. The amount of straw can be calculated as this formula:

CR: physical amount of straw, Qci: yield of Crop i, ri: Grain-straw ratio of Crop i.
Table 1: Grain-straw ratios of different crops
Rice

WheatCorn

Grain

Sorghum

Soybean

TubersOil crops

Hemp

Beet

1

1.1

2

1.5

2

1.7

1

3

1.7

0.1

Table2: Reserve of straw in Heilongjiang Province Unit: tCity

physical amountacquirable amountamount for energy use

Harbin24257373

20618767

14639325

Qiqihar17846442

15169476

10770328

Jixi

383483732596112314324

Hegang1174214998082708638

Shuangyashan

4144806

3523085

2501390

Daqing960337081628655795634

Yichun12405101054434

748648

Jiamusi

894381776022445397594

Qitaihe12758381084462

769968

Mudaniang

471220340053732843815

Heihe

3884080

3301468

2344042

Suihua24044669

20437969

14510958

Total amount

104962159

89217836

63344664

3. Comprehensive evaluation of straw utilization
3.1 Object of study
The purpose of the research is focused on a 2MW straw gasification power generation station in Heilongjiang Province.
The paper collected the technical data, equipment manufacturing data, environmental data, resource data, etc. and establisheda complete LCA database. Based on the database, the life cycle assessment of 1MW straw gasification power generation
system is made.
3.2 Assessment boundary
This paper selected the 2 MW fluidized bed straw gasification power generation system as the research object. The
technological process is shown in picture 1. The annual electricity generation amount of this system is 16million kWh. The
lifetime of the plant is set as 20 years and the functional unit is 10000 kWh. In order to generate 10000kwh electricity, theconsumption of rice is 16t. The system is composed by four processes as straw collection, straw gasification, gas purificationand electricity generation.

Fig.1 Sketch map of straw gasification power generation system
The life cycle boundary of the system is mainly divided as 5 unit process: 1. material capture process; 2. equipment andmaterial production process; 3. planting process; 4. transportation process; 5. gasification power generation process.
3.3 Inventory analysis
The inventory analysis of this paper adopted 10000kWh electricity energy as the functional unit. The input and output
inventory of generating 10000kWh electricity is shown in Table3 and the type of environment impact and equivalent factors
in LCA system are show in Table 4.
Table 3 Inventory of straw gasification power generation system

Input

Items

Average value

Unit

Rice

16t

Conventional power

0.053

GJ

Crude oil

12.6

GJ

Fuel oil

0.26

GJ

Gas

3.6

GJ

Diesel

2.4

GJ

Pipeline transport

0.12

kt km

Water

19.1

t

CO2(Whole life cycle)

7745

kg

470kg

CO

0.75kgSO2

2.52kgCO2(Not including power plant
Outputoperation)

NOX3.56kg

NMHC

0.47kgDust

1.78kg

BOD50.02kg

COD

0.05kgSS

12.85kg

NH3-N

1.34kgTar

1.01kg

Ash7500

kg

Table 4 Type of environmental impact and factors in LCA system
Material
Influence type

Unit

Equivalent factor

CO2CH41kg CO2/kg

21NOX

320

N2O

290

SO21Acidification potential

NOX

KgC2H4/kg

AP

NH3

1.88

Formaldehyde

0.421

NMHC

0.03770.7

Photochemical

VOC

ozone formation potential

Benzene

0.189

POCP

Toluene0.563

CO0.012

SO21.2NOX

0.78

Human toxic potential
HTP

Smoke and dust potential
Dust-P

BaP

KgC2H4/kg

1

KgC2H4/kg

1.7

Benzene3.9

Toluene

3.9

Naphthalene

3.9

Smoke and dust

1Fly ash

Kg dust/kg

1

Mud

1

3.4 Environmental impact assessment of life cycle
The result of inventory analysis is divided according to environmental impact to calculate various environmental impact
potential. After standardization and weighted, different environmental impact can be compared. At the same time, thecharacteristics of environmental impact from different processes of the system can be analyzed. Environmental impact
potential refers to the sum of all the impacts of similar pollutant emission within the system. The calculating formula isEP(m)=∑EP(m)n=∑[Q(m)n· EF(m)n ](2)EP(m): Environmental impact potential m, EP(m)n: Environmental impact potential m of Pollutant n, Q(m)n: Emission

amount of pollutant n, EF(m)n: Coefficient of environmental impact potential m of Pollutant n.
3.5 Standardization and weighted assessment results
The environmental impact potentials after standardization and weighted assessment were added according to classificationand finally the environmental impact index was acquired[6]. This paper calculated 12 kinds of environmental impact index.
The weighted results of environmental impact potentials of straw gasification power generation system are shown in Fig. 20.35
0.3
0.25
0.2
0.15
0.1
0.05
0GWP

APPOCP

HTP

Dust-pFig. 2 Weighted results of environmental impact potentials of straw gasification power generation system
3.6 Discussion and conclusions
Among all kinds of environmental impacts generated from the system, the photochemical smog potential is the largest. The
second is human toxicity potential. These two large potentials are due to the emission of high concentration of tar. Global
warming potential mainly comes from the operational process. If the carbon cycle characteristic of straw is consider, namely
the CO2 emission is neglected, it can be considered that the CO2 of the system is mainly from transportation period.
According to life cycle assessment data of LCA coal-fired power generation system[7], about 10 tons CO2, 80kg SO2 and50kg NOx is emitted into the atmosphere by generating 10000kWh electricity. The analysis results of this paper shows thatstraw gasification system emitted 7.7 tons CO2, 2.52kg SO2 and 3.56kg of NOx by generating 10000kWh electricity. These
data indicates that straw gasification electric generation is a kind of environmentally friendly energy production mode

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