Shell and Tube Heat Exchangers Used as Flue Gas Heaters

Shell and tube heat exchangers consist of a housing and a number of internal tubes through which the flue gases flow while the heating medium (e.g. water or oil) flows in the housing. Through the exchange of heat between the two fluids, the heat from the flue gas is effectively transferred to the heating medium.

Principle of operation

Flue gas flow: High temperature flue gas is discharged from the boiler, burner or other equipment and enters the shell and tube heat exchanger.

Heat exchange: the flue gas flows in the tube and exchanges heat with the heating medium flowing in the shell, the temperature of the flue gas decreases while the temperature of the heating medium increases.

Emission and utilisation: The heated medium can be used for heating, process heating or other purposes, while the cooled flue gases are discharged to the atmosphere.

Design Considerations

Material selection:

High temperature and corrosion resistant materials (e.g. stainless steel or alloys) need to be selected to ensure stability in high temperature flue gas environments.

Piping Layout:

Optimise the number and arrangement of pipes to maximise the heat exchange area and ensure good heat transfer efficiency.

Fluid flow:

The flow pattern within the pipework (e.g. turbulent or laminar) affects the heat exchange efficiency and flow resistance and pressure drop need to be taken into account in the design.

Maintenance and Cleaning:

The design should take into account ease of cleaning and maintenance to prevent dirt and deposits in the flue gas from affecting performance.

Temperature Control:

The temperature of the flue gas and media should be monitored and controlled to ensure that the system operates within safe and efficient operating limits.

Applications

Boiler systems: Recover heat in the flue gases emitted from boilers to improve overall thermal efficiency.

Industrial Furnaces: Provide preheated air or water to industrial furnaces to reduce energy consumption.

Power plants: Used in coal-fired or gas-fired power plants to recover heat from exhaust gases and improve power generation efficiency.

Environmental facilities: Used in flue gas desulphurisation or dust removal systems to help reduce greenhouse gas emissions.