Key Components of a Heat Recovery Boiler Heat Exchanger

Key Components of a Heat Recovery Boiler Heat Exchanger:

1. Tube Bundles

Heat Transfer Surface: The core of the heat exchanger is made of tube bundles through which the working fluid (usually water) flows. The tubes absorb heat from the exhaust gases or flue gases passing over them.

Materials: The tubes are typically made of high-temperature resistant materials, such as carbon steel, stainless steel, or alloys like Inconel, depending on the operating conditions.

Water or Steam Flow: Water enters the tubes and is heated by the hot gases flowing over the tubes, causing it to convert into steam, which can be used for power generation or process heating.

2. Finned Tubes

Finned Design: To increase the heat transfer surface area, the tubes are often finned. Fins improve the efficiency of heat transfer by maximizing the contact between the exhaust gases and the tube surface.

Materials and Type: Finned tubes may be made from carbon steel, stainless steel, or other corrosion-resistant materials, depending on the exhaust gas composition and temperature. Fins can be spiral-wound or extruded for improved heat transfer efficiency.

3. Economizer

Preheating the Feedwater: An economizer is a heat exchanger located in the HRB system, designed to preheat the feedwater before it enters the boiler. This increases the overall efficiency by reducing the amount of fuel needed to heat the water to the required temperature.

Types of Economizers: There are bare-tube economizers and finned-tube economizers, depending on the heat transfer requirements.

4. Evaporator

Phase Change from Water to Steam: The evaporator section of the heat exchanger is where the water absorbs heat and converts into steam. The evaporator is often equipped with extended surfaces, such as finned tubes, to maximize heat absorption.

Natural or Forced Circulation: In some systems, water circulates naturally due to density differences (natural circulation), while in others, pumps may be used to force water through the tubes (forced circulation).

5. Superheater

Superheating the Steam: After steam is generated in the evaporator, it often passes through a superheater, which further increases the steam temperature beyond the boiling point at a given pressure. Superheated steam is preferred in power generation because it reduces the likelihood of condensation in turbines and improves thermal efficiency.

Superheater Tube Material: Since the superheater handles very high temperatures, it is usually constructed from heat-resistant alloys such as stainless steel or Inconel.

6. Preheater or Air Heater

Preheating Air for Combustion: In some HRBs, an air preheater is used to warm the air entering the combustion chamber, which improves fuel combustion efficiency. The preheater is another type of heat exchanger that transfers heat from exhaust gases to incoming air.

Rotary or Tubular Air Heaters: These can either be rotary, where a rotating matrix of heat-absorbing material captures heat from exhaust gases and transfers it to the air, or tubular, where air flows through tubes and is heated by exhaust gases flowing over the tubes.