Research status

1.2.1.1 Different biomass for co-combustion

Biomass includes forest wastes, agricultural wastes, animal wastes and anthropomorphic wastes. Considering co-combustion with straw and coal could achieve large-scale and efficient utilization, it is attracting more and more attention and research. Most methods for research are concentrated in the laboratory using thermal gravimetric analysis, or measuring the combustion characteristics of mixtures of pollutants (including toxic gases and heavy metals, etc.) emission characteristics and ash melting characteristics through combustion or pyrolysis of different coals and biomass. The conclusions gained through these methods are an important reference for the design calculations and material choices of biomass-fired boilers, but the site condition is quite different from the experimental condition.

(1) Co-combustion ofcoal and agricultural wastes

In the Northeast Institute of Electric Power Engineering, experimental research on co-combustion of coal and corn stalk were carried out (Lu et al., 2005). The results showed that the co-combustion of coal and corn stalk was helpful for coal burnout. With the increase of co-combustion rate from 20% to 80% (mass biomass to coal ratio), the burnout efficiency was increased, the burnout time was shortened and the burnout temperature was decreased. In Shandong Univer­sity, Zhang et al. (2006) researched on the characteristics of straw co-combustion with coal by the thermal gravimetric analysis method. Cotton stalk, cornstalk, wheat-straw were chosen for co-combustion with coal at different heating rate (30, 50, 75 and 100K/min) and different co-combustion rate (1:20,1:10, 3:20,1:5,1:4, 3:10). The results showed that the co-combustion of coal and straw was helpful for coal burnout. With the rise of heating rate, the ignition temperature of straw mixed coal was decreased and the rate of combustion was increased.

In order to making clear the effect of the alkali metal K on nitrogen conversion in co-combustion of coal and straw, a series of experiments were carried by Yang et al. (2009). The results indicate that it is effective to inhibit the release of NO to add a certain proportion of straw. When the content of K increases in the de-ashed coal samples mixed with a low proportion of straw and KOH, it has a stronger catalytic effect on the reduction reaction of NO, and when the content of K reaches a certain value, the catalytic effect does not increase. The lower the O2 content in the combustion atmosphere, the better the reduction of NO. Dong etal. (2010) have taken some experimental tests. The experiments were carried out at a 400 t/h power station boiler to test its economy and emission characteristics. Considering each operation controllable factor, the best running condition were optimized, which could keep better economy and emission performance. The optimized condition consisted of oxygen content 3.6%, combustion temperature 1278K, pulverized coal fineness R90 = 20%, straw particle size 15 mm, primary air with average coordination, secondary air with waist type, and co-combustion ratio 20% (a heat ratio value). [3]

Table 4.2. Volume of garbage disposal and treatment plants in China (2010).

Region

Area under cleaning program 10000 m2

Volume of garbage disposal 10000 tonnes

Number of treatment plants/grounds unit

Sanitary

landfill

Compost

Burning

National total

485033

15804.8

628

498

11

104

Beijing

13804

633

20

15

3

2

Tianjin

7322

183.7

8

6

2

Hebei

20050

589.3

26

20

4

Shanxi

10609

361.2

17

14

3

Inner Mongolia

9674

334

18

17

1

Liaoning

28122

837.3

25

24

1

Jilin

13037

499.4

7

5

2

Heilongjiang

14937

782.4

20

17

2

Shanghai

15879

732

12

4

2

3

Jiangsu

44088

1017.1

44

30

14

Zhejiang

27805

959

52

30

22

Anhui

17339

435.3

16

13

3

Fujian

11433

417.3

20

14

6

Jiangxi

9911

284

13

13

Shandong

48528

992

55

46

8

Henan

20892

694.6

38

35

1

2

Hubei

16941

711.1

23

21

1

Hunan

12331

505.2

21

21

Guangdong

62768

1938.6

41

25

16

Guangxi

11005

245.1

20

16

1

3

Hainan

4076

97.7

3

2

1

Chongqing

6136

256.7

13

12

1

Sichuan

15173

656

30

23

5

Guizhou

3405

213.3

12

12

Yunnan

9726

265.5

19

12

2

3

Tibet

539

16.3

Shaanxi

10546

388.3

15

11

1

Gansu

5816

278.3

13

13

Qinghai

1951

86.3

3

3

Ningxia

3347

91.9

7

7

Xinjiang

7843

303.3

17

17

Note: Data from National Bureau of Statistics of China.

is 0.3876 million tonnes, the proportion of treated garbage (%) is 77.9%, all which are shown at Table 4.2, Table 4.3 and Table 4.4.

As shown in Figure 4.2, garbage disposed by burning isn’t the most important way in China, which takes 22% and less than other disposing ways e. g. sanitary landfill. Incineration is a waste treatment process that involves the combustion of organic substances contained in waste materials (Andrew, 2005). Incineration can reduce the solid mass of the original waste by 80-85% and the volume (already compressed somewhat in garbage trucks) by 95-96%, depending on composition and degree of recovery of materials such as metals from the ash for recycling (Ramboll, 2006).

In China, researchers have focused on co-incineration performance tests and experiments of coal and different types of MSW Gu et al. (2003) focused on the co-combustion research of municipal sewage sludge and coal. With a thermogravimetric method, the research results showed that co-combustion could enhance activation energy with a lowering of the ignition temperature.

Table 4.3. Quantity of waste treated in China (2010) (Unit: million tonnes).

Region

Quantity of waste treated

Sanitary

landfill

Compost

Burning

City sanitation special vehicles (unit)

National total

12317.8

9598.3

180.8

2316.7

90414

Beijing

613.7

445.4

79.3

89.1

7461

Tianjin

183.7

125.4

58.3

1951

Hebei

411.5

311.6

58.9

3306

Shanxi

265.8

213.5

52.3

3689

Inner Mongolia

276.5

251.7

24.9

1480

Liaoning

593.5

571.6

21.9

4998

Jilin

222.3

172.4

49.9

2608

Heilongjiang

315.7

284.6

16.6

3814

Shanghai

599.2

416.5

21.2

108.1

5560

Jiangsu

951.7

488.5

458.7

7481

Zhejiang

942.7

504.9

437.8

4685

Anhui

281

231.1

49.9

1508

Fujian

383.8

241.7

142

2036

Jiangxi

243.9

243.9

899

Shandong

911.6

751.9

131.4

5983

Henan

573.7

501

6.9

65.7

3025

Hubei

436.9

405.8

18.4

3077

Hunan

399.1

399.1

1998

Guangdong

1398

1031.6

366.4

8535

Guangxi

223.3

203.5

9.3

10.5

1748

Hainan

66.4

61.6

4.8

1525

Chongqing

253.7

216.3

37.4

1786

Sichuan

569.8

464.3

7

80.8

3301

Guizhou

193.3

193.3

882

Yunnan

234.4

123.2

10.4

77.7

1783

Tibet

20

Shaanxi

310

281.2

2.2

1719

Gansu

105.6

105.6

1045

Qinghai

58.1

58.1

330

Ningxia

85

85

554

Xinjiang

214

214

1627

Note: Data from National Bureau of Statistics of China.

The fuels have basically attained devolatilization characteristics in the co-combustion process. Liu’s (2006) experimental research showed that the reactivity of the blend with 20 wt. % of sludge is similar to that of coal. When the blend is with 50 wt. %, there are two temperature zones with obviously different reactivity trends. In the lower temperature zone (less than 430°C), the reactivity of the blend is similar to that of the sludge, and in the higher temperature zone (greater than 430°C), the reactivity of the blend is close to that of the coal. Zhao etal. (2005) researched on co-combustion of sludge/residue in a paper mill with high moisture content and low heating value coal at the hot circulating fluidized bed test facility. His research showed that when the secondary air rate increases, temperature in the dense bed decreased slightly and temperature in the dilute phase region declined, while the combustion efficiency was increased. When the excess air coefficient was increased, temperature in the dense bed increased, temperature in the dilute phase region increased at first and then declined forming an optimum value corresponding to the highest combustion efficiency. When the ratio of paper mill waste to coal was increased, the decline in temperatures in both dense bed and dilute phase region was decreased, and the combustion efficiency was decreased. Lu et al. (2004a) indicated that co-combustion of sewage

Table 4.4. The waste treatment capacity (tonne/day) in

China (2010).

Region

Treatment capacity (tonne/day)

Sanitary

landfill

Compost

Burning

Proportion of treated garbage (%)

National total

387607

289957

5480

84940

77.9

Beijing

16680

12080

2400

2200

97

Tianjin

8000

6200

1800

100

Hebei

13614

10064

2450

69.8

Shanxi

10568

7968

2600

73.6

Inner Mongolia

9167

8367

800

82.8

Liaoning

17247

16647

600

70.9

Jilin

6496

4456

2040

44.5

Heilongjiang

10969

9869

500

40.4

Shanghai

10545

5750

520

2575

81.9

Jiangsu

37637

22445

15192

93.6

Zhejiang

33323

16438

16885

98.3

Anhui

9420

7670

1750

64.6

Fujian

12747

7197

5550

92

Jiangxi

6066

6066

85.9

Shandong

35225

26425

8200

91.9

Henan

20416

17616

400

2400

82.6

Hubei

12800

11400

1000

61.4

Hunan

11818

11818

79

Guangdong

33956

22213

11743

72.1

Guangxi

8191

6871

400

920

91.1

Hainan

1764

1539

225

68

Chongqing

6465

5265

1200

98.8

Sichuan

16974

13334

2340

86.9

Guizhou

5697

5697

90.6

Yunnan

7749

3849

360

2870

88.3

Tibet

Shaanxi

10707

9347

500

79.8

Gansu

3355

3355

38

Qinghai

931

931

67.3

Ningxia

2785

2785

92.5

Xinjiang

6295

6295

70.6

Note: Data from National Bureau of Statistics of China.

■ Burning;

image157

Figure 4.2. Percentage of different garbage disposal methods in China (2010).

sludge with coal on a circulating fluidized bed was stable at water contents of 30-60% in sewage sludge and co-combustion rates of 25-100%.

Co-combustion of coal and refuse derived fuel (RDF) were carried out in a bubbling fluidized bed combustor by Sun et al. (2006). The feasibility of solidification and co-combustion of waste

image158

Figure 4.3. Biomass co-combustion system.

products in oily wastewater with coal was analyzed by Liu et al. (2005). The combustion process, ignition and burnout characteristics of waste tire and coal with a tire-coal ratio of 10%, 30% and 50% were investigated by means of thermogravimetric analysis (TGA), which were carried out by Li etal. (2007), whose research showed that co-combustion with waste tires could improve the burnout characteristics. Co-combustion of waste plastic and coal in fluidized bed were researched by Jin et al. (2001) and co-combustion of Medical Solid Waste and coal in a CFBC by Pu Ge et al. (2003).

Добавить комментарий

Ваш e-mail не будет опубликован. Обязательные поля помечены *