Bagasse Fired Boiler is commonly known as bagasse boiler. Bagasse is the residue after sugar refinery and it is similar to wood in chemical composition. The annual yield of bagasse is over 18 million tons in China, and the main purpose is for paper making and fuel. Bagasse features light weight, high volatile matter, high moisture, high sulfur content, low heating value, low ash fusion point, etc.

I. Bagasse Fired Boiler combustion characteristics

  1. High water content results in high requirement for drying, low heating value and poor combustion stability, more fine powder is difficult to burn off.
  2. High ash content and light weight, more suspended fines in the flue gas, and severe ash deposition in the heating area.
  3. The majority of fuel is burnt in a suspended state, the combustion flame is long and combustion demands sufficient height.
  4. Low ash fusion point and easy-coking.
  5. High sulfur content causes low-temperature corrosion, and certain alkali metal may cause high-temperature corrosion.
Design of One 150ton Bagasse Fired Boiler
Design of 150ton Bagasse Fired Boiler

II. Key technical points in Bagasse Fired Boiler design

  1. Combustion mode: based on above combustion characteristics, this 170t/h bagasse fired boiler adopts grate combustion. Most importantly, chain grate is not easy to have coking problem, moreover, the ash and slag removal is good.
  2. Feeding mode: due to high moisture and fine powder, so this biomass boiler adopts hot air pneumatic spraying feeding. The spraying device is in the front wall; the bagasse is heated and dried by flue gas during spraying. Bagasse is burnt in a suspended state after being mixed with the primary air from the bottom.
  3. Grate operation mode: chain grate operates in a reverse direction, namely from back to front. The bagasse is heated and burnt during spraying, while the unburned bagasse is burned on the grate.
  4. Arrangement of secondary air: secondary air ensures good penetration, supplements the oxygen, and promotes the bagasse burnout. In addition, staged air supply restrains the generation of NOx.
  5. Arrangement of heating area: large furnace volume prolongs the flue gas retention time and ensures the burnout of bagasse. The water wall is with refractory baffle to maintain high temperature combustion and make for the ignition. Furnace outlet temperature is around 812℃, lower than the ash fusion point, thus lowering the possibility of coking.
  6. Air preheater design: air preheater has three stages. A multi-clone dust collector is ahead of the final stage, which can prevent low-temperature corrosion.
  7. Anti-wear heating area: the flue gas velocity is lower than 11m/s, superheater structure is reasonable, pipe wall temperature is low, which reduces the abrasion. To prevent ash deposition, the superheater and convection tubes have soot blowers.
Design of 150tph Bagasse Fired Boiler

III. Bagasse Fired Boiler specification and structure

  1. Bagasse Fired Boiler specification:

Capacity: 150t/h

Rated steam pressure: 9.8MPa

Rated steam temperature: 540℃

Feed water temperature: 158℃

Continuous blowdown rate: 2%

Cold air temperature: 20℃

Design thermal efficiency: 89.2%

  1. Bagasse Fired Boiler general arrangement:

TG-150/9.8-T biomass boiler is a single drum natural circulation full suspension membrane wall chain grate boiler.

  • Furnace and combustion device

Furnace height is around 23m, and the water wall is rectangular shape comprising Φ60×5 pipe and flat bar. Chain grate is in the bottom of furnace, and primary air box is below the grate. Six sets of bagasse spraying devices are in the front wall, including slag tube, jet case and angle adjustment device. Grate is cross-girder rotary grate.

  • Superheater and desuperheater

Superheater includes roof tube, wall enclosure tube, low-temperature superheater, primary desuperheater, medium-temperature superheater, cold high-temperature superheater, secondary desuperheater and hot high-temperature superheater.

  • Economizer

Economizer is in the tail part, composed of two stages. Water flows through the inlet header of lower economizer, coil tube bank of upper economizer and drum.

  • Air preheater

Air preheater has three stages tube boxes. The first two stages adopt Q310GNHA tube while last stage adopts SS304 tube.

  • Soot blower

Superheater and convection tube have soot blower, which ensures clean heating area and safe operation.