Corner Tube Type Hydrogen Boiler Design

Corner tube type hydrogen boiler is an advanced gas fired boiler type imported from abroad. The furnace part is full membrane wall structure. The convection heating area adopts flag pattern heating surface structure. It features small air leakage coefficient, compact structure, safe and reliable water circulation.

1. Hydrogen fuel analysis

Hydrogen has many differences from natural gas, manufactured gas and biogas, as follows:

1.1  Light specific gravity: hydrogen is the lightest gas known in the world. Its density is very small, only 1/14 of the air. Residual unburnt hydrogen is easily accumulated in the headspace of dead angle of flue gas.

1.2  Fast burning and extremely explosive: the ignition temperature is 400°C, and the burning speed is about 8 times of natural gas. When the concentration of hydrogen in the air is within 4-74.2%, it will immediately explode when catching an open fire. Therefore, the hydrogen deflagration problem is the top priority in the design of hydrogen boiler.

1.3  High combustion temperature: the flame temperature can reach 2000 ℃ during combustion. Keeping safe water circulation in the heating tube is also the key to safe operation of hydrogen boiler.

1.4  Large water content in the flue gas: hydrogen becomes water after burning, and water becomes vapor after absorbing the heat from combustion, which increases the flue gas amount. The increase of vapor in the flue gas improves its dew point temperature. The flue gas temperature of hydrogen boiler is generally above 150°C to avoid oxidative corrosion due to condensate under low load.

2. Current status of hydrogen boiler

Hydrogen boiler can be divided into LHS gas fired boiler and SZS gas steam boiler. LHS gas boiler has a maximum evaporation capacity of 2t/h, and SZS gas steam boiler has a maximum evaporation capacity of 6t/h and above.

LHS gas fired boiler adopts vertical layout structure. The body heating surface is a combination of water tube and fire tube. The radiant heating surface is composed of water wall. Inner water wall tube and outer downcomer form natural circulation loop. The lower and upper part of water wall and downcomer is connected to header and lower tube plate of drum. Convective heating surface is the flue gas pipe in the drum shell. An economizer is arranged above the corner tube boiler body, and a burner is at the bottom. The flue gas flows from the bottom to the top.

SZS gas steam boiler has a full membrane wall furnace, the furnace section is “D” type, also called D type boiler. The front wall of furnace is with a burner. After passing through the furnace, the flue gas enters the convection heating surface. The convection heating surface is composed of tube bundle connecting upper and lower drums. The flue gas finally discharged from the tail of convection heating surface.

3. Corner Tube Boiler Design

3.1  Design parameter

Item

Unit

Value

Rated evaporation

t/h

4.0

Feed water temperature

20.0

Design efficiency

%

91.9

Steam pressure

MPa

1.0

Saturated steam temperature

184

Fuel consumption

Nm3/h

1105

Flue gas temperature at furnace inlet

2011

Flue gas temperature at furnace outlet

1112

Flue gas temperature at convection tube bundle inlet

1112

Flue gas temperature at convection tube bundle outlet

793

Flue gas temperature at spiral fin tube bundle inlet

793

Flue gas temperature at spiral fin tube bundle outlet

341

Flue gas temperature at economizer inlet

341

Flue gas temperature at economizer outlet

160

 

3.2  Type selection

The design fully retains the advantage of corner tube boiler in water circulation. Considering low density, an optimized modification is performed on the basis of the DZL coal fired boiler.

3.3  Design of DZS hydrogen steam boiler

Main task is to arrange the furnace and heating surface structure, ensure stable combustion, safe and efficient heating surface. How to improve the safety is the focus of this design.

3.3.1 Flue gas flow design

It adopts straight-through flue gas process, and burner is at the front wall of furnace. After combustion, hydrogen passes through light pipe convection tube bundle, spiral fin tube bundle and economizer tube bundle. The top of flue duct is horizontal and straight, convenient for soot blowing and not easy to generate dead angle.

3.3.2 Furnace design

The cross section of furnace is in a “「」” shape. The upper and lower headers are shared by membrane wall. Saturated water enters from left lower header and flows to right upper header.

A spring-type explosion door is on the top of furnace, which can quickly reduce the pressure when furnace deflagrates.

3.3.3 Convection heating surface design

The flag pattern heating surface tube bundle is a feature of corner tube boiler. One end is welded to membrane wall tube and the other end is on the supporting tube. When flue gas flows from top to bottom, it can maintain the stability of heating surface tube.

3.3.4 Economizer design

In order to further reduce flue gas temperature, spiral fin tube economizer is at the end of the steam boiler. A header tank is at the bottom of economizer, draining condensate under low load.

3.3.5 Design of other parts

This corner tube boiler uses a hydrogen fired burner from South Korea. The burner functions stream diversion, forced mixing, load regulation and linkage control. The combustion rate of hydrogen can reach 100%. The burner is also with high pressure, low pressure, cut-off, leak detection, venting, pressure stabilization, anti-flaming and other systems.

Corner Tube Type Hydrogen Boiler Design01


Post time: Mar-27-2020