The Exhaust gas economizer in a ship is a feed-water heater in which the heat from waste gases is recovered. It raises the temperature of feed water supplied to the marine boiler.
It is like a huge heat exchange that exchanges heat between exhaust gas from engines to water and produces steam for the same purpose that auxiliary boilers produce steam.
An exhaust gas economizer is a type of heat exchanger that is installed in the exhaust gas system of a marine diesel engine. Its primary purpose is to recover waste heat from the engine’s exhaust gas and use it to preheat the feedwater for the ship’s boilers, thereby improving the overall efficiency of the ship’s propulsion and power generation systems.
The exhaust gas economizer works by transferring heat from the exhaust gas to the feedwater, which is circulated through the economizer by a pump. As the feedwater is preheated, less energy is required to bring it up to its boiling point, which reduces the amount of fuel needed to produce steam in the ship’s boilers.
By recovering waste heat that would otherwise be lost, the exhaust gas economizer can improve the overall efficiency of the ship’s propulsion and power generation systems, which can lead to significant fuel savings and reduced emissions. This is particularly important for large commercial vessels, such as container ships and oil tankers, which consume large amounts of fuel and produce significant amounts of greenhouse gas emissions.
In summary, an exhaust gas economizer is a heat exchanger that recovers waste heat from a marine diesel engine’s exhaust gas and uses it to preheat the feedwater for the ship’s boilers, thereby improving the efficiency of the ship’s propulsion and power generation systems and reducing fuel consumption and emissions.
The purpose of the exhaust gas economizer is to increase plant efficiency by removing heat that would otherwise be lost in the flue gas and using it to indirectly heat the feedwater for the marine boiler.
Heating the feed water it is also helping to prevent thermal shock as the water enters the steam drum.
Table of Contents
What is exhaust gas economiser (EGE) Fire and how does it occur?
- A flame appears at the economizer coil during the running of the main engine at sea while the EGE is put into service with circulation water passing through the coils, it is called economizer fire.
- It is actually caused by soot fire at the economizer coils.
- For the economizer coils fire, heat is already presented due to passing the gases of the main engine.
- Air is available due to an excess supply of scavenging air into the unit combustion chamber.
- A thick deposit of unburnt fuel and carbon residue (soots) are sticking to the economizer coils.
- Soot is formed from incomplete combustion and the use of low-grade fuel and high carbon content fuel.
- At the maneuvering time, the more incomplete combustion may occur, and at that time leaving flue gas velocity is very low, thus unburnt fuel can adhere to the economizer coils.
- A flame is produced when air and fuel are proportionally mixed at a sufficient heating temperature.
What are the actions to be taken during an economizer fire?
- Inform the bridge and chief engineer. Take the permission to stop the main engine.
- Gradually slow down the ME and then stop.
- If fire fighting equipment is fitted, it should be brought into operation.
- Cooldown the economizer by means of boundary cooling.
- The circulation pump must be run but, if a large amount of water is lost it must be stopped.
- There is no heat source and the fire is out.
- When economizer fire occurs never do soot blow to economizer.
- It can cause hydrogen fire and the meltdown of the coils stack. It can cause deformation and tube bulking because intensive heat and high thermal stress are formed at economizer coils.
What are the indications of EGE fire?
- Smoke smell will get from the economizer.
- Overheat at economizer body ( external casing of uptake.)
- Heavy smoke and sparks will emit from the funnel.
- Sudden unexpected increase in uptake gas temperature ( Abnormally high stack pyrometer reading)
- Flame is visible in the smoke indicator.
How to prevent EGE fire on ships?
- To get complete combustion of fuel, maintain the main engine (ME) in optimum combustion condition.( governor, fuel injection pump, fuel injection valve, fuel injection timing, fuel condition, air cooler, turbocharger, do not run too long ME with slow speed)
- Regular open up & cleaning smoke side of economizer depending upon soot accumulation. (water washing)
- Regular soot blowing operation. Check & maintain soot blowing equipment.
- Regular overhaul boiler burner, correct air-fuel ratio & damper.