Designing A Boiler Chimney heat recovery System Against Fouling – Mechanical Project

ABSTRACT

An initial design of chimney heat recovery heat exchanger was provided. The design had a completely fabricated exchange core but an incomplete ducting system .

This report is based on the work undertaken to complete and test the gas to gas heat recovery system. This system was specifically designed for boiler chimney and therefore the systems ducting was designed to conform to the general boiler stack. In the completion of the design, the major factor to consider was to design against fouling. The system was therefore designed with means of reducing fouling such as provision for easily replaceable particulate filter and quick washing system.
The project was hence done in the following manner.
1. Completing of the fabrication.
2. Research on ways of minimizing fouling .
3. Incorporating the ways arrived at in 1 above into the system design.
4. Testing of the model under forced convection condition.
The gases from a furnace were used to simulate industrial flue gases. The performance of the model was used to project the optimum of prototype.

OBJECTIVE STATEMENT
The aim of this project was to recover heat lost through flue gases exhaust at the chimney stage taking a keen consideration of the effect of fouling especially at the core of the heat exchanger.
Some research was done and the exchanger system designed and fabricated though not to completion. It was nevertheless tested specifically to determine its heat exchange effectiveness.
However critical factors such as fouling were not keenly observed. The small plate spacing of the exchange core will allow for a substantial heat recovery. This obviously means the core will undergo fouling at a higher rate as compared to boiler tubes. This makes the exchanger to require more frequent maintenance than the normal boiler maintenance.
The objective was to review the design ensuring that fouling was reduced and that the maintenance practice on the exchanger does not adversely interfere with the normal operation of the boiler.
It was projected that the project will maintain its goal of recovering heat and hence its benefits towards energy management and at the same time maintain the smooth operation of the boiler.

The aim of this project can therefore be summarized as
1. Complete the fabrication of the heat recovery system and test.
2. Research on fouling effects for different fuels used in boilers.
3. Minimizing fouling and reduce maintenance requirements to avoid interference with the normal operations of the boiler.
4. Give the recommendations based on the prototype performance

Designing A Boiler Chimney heat recovery System Against Fouling

DESIGN CONSIDERATIONS
In the designing of the exchanger following factors were put to consideration.
1. The exchanger surface has to be the most efficient and suitable for gas-gas heat exchange.
2. The design has to consider the fouling effect of the flue gases.
3. The design has to allow for quick maintenance without interfering with the boiler operations.
4. The ducting design has to conform to the boiler chimney design.
Based on the above factors, the exchanger was designed to be of compact plate type. Various designs for the exchange core were considered including cylindrical type (ducts). The plate type was found to be more efficient and simpler in design. It was also more suitable for gas – to gas heat exchange as it offers higher surface for heat transfer.