Design of Reciprocating Grate Biomass Industrial Boiler

Taishan Boiler

Biomass Industrial Boiler is one kind of biomass boiler used for industrial production. Biomass fuel has two types: one is biomass waste such as grain straw and sawdust bark, the other is pellet.

I. Biomass Industrial Boiler Fuel Characteristics

Item

Sugarcane leaf

Cassava stalk

Straw

Bark

Tree root

C / %

43.11

16.03

39.54

35.21

36.48

H / %

5.21

2.06

5.11

4.07

3.41

O / %

36.32

15.37

32.76

31.36

28.86

N / %

0.39

0.34

0.74

0.23

0.17

S / %

0.18

0.02

0.16

0.00

0.00

A / %

4.79

0.98

7.89

2.13

7.71

W / %

10.0

65.2

11.8

27.0

30.0

V (dry ash-free basis) / %

82.08

82.24

80.2

78.48

81.99

Q / (kj/kg)

15720

4500

14330

12100

12670

1. Lower heating value of biomass fuel is different due to different moisture content, while higher heating value is similar. The fuel accumulated outdoors has a moisture content ranging from 12% to 45%.

2. Biomass fuel has high volatile content. Biomass fuel starts pyrolysis when temperature exceeds 170°C, 70%-80% of volatile matter is precipitated, including H2O, CO and CH4.

3. Biomass fuel has no fixed ash melting point. Al, Fe, Ca, Mg and other oxides in the ash increases the ash melting point. However, high K and Na content makes the ash melting point lower than that of coal.

4. Biomass fuel ash has a low density and is easier to be carried by the flue gas. In addition, slagging is easy to form on the convective tube bundle, which affects the heat transfer effect.

5. The overall dimensions of biomass fuel are irregular.

II. Biomass Industrial Boiler Design

1. Selection of combustion equipment

Reciprocating grate has obvious advantages over chain grate in fuel size and fuel leakage. So reciprocating grate becomes a reasonable choice for biomass layer combustion equipment. Inclined air-cooled reciprocating grate is an economical and effective combustion equipment for biomass combustion.

2. Design of feeding device

The bulk density of biomass fuel is about 200 kg/m3 and the thickness of fuel layer is over 20 cm. The operating temperature of fuel silo in front of furnace shall be below 150°C. A sealed gate is at the feeding port. The temperature reduction and fire protection can be water cooling jacket.

3. Design of furnace

Recommend to adopt a fully-sealed steel structure, steel plate as outer shell, lined with insulation cotton and heavy refractory materials. The front and back arch and side walls of furnace are all heavy refractory materials. The residence time of flue gas in the furnace shall be at least 3m/s.

4. The proportion of air distribution

Primary air is from lower part of the grate, and is divided into preheating zone, combustion zone, and slag zone. Secondary air realizes the disturbance of combustion and supply of oxygen.

Primary air volume shall be 50% of the total air volume. The air volume of primary air in preheating zone and slag zone is for cooling the grate bar. Secondary air has two parts, air supply volume accounts for 40% and distributing air accounts for 10% of total air volume. The flow velocity of distributing air is generally 40-60 m/s, and fan pressure is generally 4000 to 6000 Pa.

5. Design of heat exchange surface

Convection tube bundle shall be designed in sections, and gap between the tube at high temperature area shall be enlarged.

Biomass Industrial Boiler are common in wood industry, providing hot oil, steam, hot air for production of medium-and-high-density fiberboards.