1.2.1.2 Chuang Municipality Lutang Sugar Factory

Chuang Municipality Lutang Sugar Factory of Guangxi province improved the boiler by using a 35 t/h fluidized bed boiler for burning a mixture of coal and bagasse instead of 25 t/h pulverized — coal fired boiler. With a ratio of coal to bagasse of 60 to 40%, the project was successful (Liu et al., 2003).

Chuang Municipality Lutang Sugar Factory uses the fanlike coal pulverizer for milling in the 25 t/h pulverized coal fired boilers. The boilers are dual-drum transverse arrangement of convection bank boilers, the superheaters are arranged between slag screens with a convection bank, and economizers and air preheaters are arranged in the rear flue. Boiler design parameters: evaporation capacity of 25 t/h, vapor pressure of 2.4.5 MPa, vapor temperature of 400°C. The steam boilers produce is used to generate electricity and heating. The boilers need to burn high quality coal instead of bagasse, which is combustion by-product of virgin sugar. The boiler efficiency is not high, thus running a large consumption. Chuang Municipality Lutang Sugar Factory has an urgent requirement to transform the boilers, so that coal and bagasse can be mixed in the combustion to reduce the operating cost.

In order to expand the evaporation capacity (from 25 to 35 t/h) and mix coal with bagasse for combustion, the boilers use circulating fluid bed combustion, being a circulating fluid bed type of furnace with pipe laying. The boiler standards after transformation should be: (1) Fluidized bed boilers with coal mixed bagasse for fuel, the ratio of 60% for soft coal with 40% for bagasse. Net calorific power of soft coal is 16,747 kJ/kg, and volatile is 15.18%. (2) Boiler evaporation of 35 t/h. (3) Boiler steam with the same pressure and temperature. The detailed transformation of the boiler heating surface is shown in Table 4.6.

After the transformed boilers are put into operation, coal and bagasse are mixed to be burned (the ratio of 60% for soft coal with 40% for bagasse). Coal enters the combustion chamber through the belt feeder and bagasse enters the dilute-phase zone by pneumatic power. Coal main burns in the dense phase bed and bagasse main burns in the dilute phase bed. Evaporation capacity can

reach 30-32 t/h. Temperature under the bed is 930-980°C and at combustion chamber outlet is 680-720°. Boiler steam parameters can meet the design values and boilers run stable.