EEI has designed, manufactured and supplied Economisers with heat duty upto 3,000,000 kcal/hr.

Economisers are heat exchangers used to preheat the boiler feed water, in waste heat recovery, and cogeneration. Boiler Economizers are tubular heat transfer surfaces designed to reduce energy consumption, reduce the temperature of the exhaust gas, raise the overall thermal efficiency of the boiler, and to reduce fuel consumption.

Boiler Economizer is utilized for preheating of water. Feed water is heated by economizers before it enters the drum. Feedwater preheating helps to capture more heat from the flue gases.  Economizer reduces the potential of thermal shock and large water temperature fluctuation as the feed water enters the boiler drum.

Economizers are used in waste heat boilers and other heating and cooling equipment. Economizer used with Shell and tube waste heat boilers uses the gases from diesel generator exhaust, furnaces, gas turbines, and incinerators. Economizers can use the exhaust gases from an industrial boiler to preheat the cold water (feed water) that is used to fill the boiler

Boiler efficiency is directly related to the temperature of the feedwater. Economizer is the last water cooled heat trap, upstream of the air heater. Economizers use the enthalpy, (Enthalpy is equal to the internal energy of the system plus the product of pressure and volume), in fluid streams that are not sufficiently hot for use in a boiler. So, economizers can recover more enthalpy and improve the thermal efficiency of the boiler. In this way, economizers can serve as feedwater heaters or feedwater pre-heaters.

EEI has a complete understanding of industrial boilers for the design of economizers for optimal thermal efficiency. An economizer can be made pressurized economizer or non-pressurized economizer, steaming economizer or non-steaming economizer, condensing economizer or non-condensing economizer depending on the required water temperature.

The Economisers are designed as pressurized Economiser if the required water temperature is above the normal boiling point at atmospheric pressure. Non-pressurized economizers are needed if they are below the boiling point. Steel pipe economizers are generally used in ultra-supercritical boilers due to the high steam temperatures and pressures involved.

Steaming economizers should be designed carefully taking into consideration the enthalpy of fluid leaving economizer, enthalpy of fluid entering economizer and the enthalpy of saturated water at economizer outlet pressure. The design must be oriented so that the water flows upward and with the outlet positioned below drum level. This avoids water hammer and excessive flow instabilities.  In steaming economisers, some part of the water (about 5 to 7%) is converted into steam during its passage through the economizer. In case of Non-steaming economizers feed water is heated within 75% of the saturation temperature of the boiler.

Non-condensing Economisers are used in coal-fired thermal power plant where the temperature of the flue gas can be reduced to 120 deg C. Non-condensing Economisers increases the efficiency of the boiler by 3-6%. Condensing Type Economisers are used in natural gas-fired thermal powerplant. Condensing Economisers can reduce the flue gas temperature below condensation temperature as low as 25 deg C and also increases the boiler efficiency by 10-15%. Condensing economizers are more suitable for non-sulphur based fuels.

Economizers in thermal power plants are sized for the volume & temperature of flue gas, the maximum pressure drop passed the stack, fuel type and the amount of energy that needs to be recovered.

Economizers are usually counter-flow heat exchangers for recovering energy from the flue gas.

The information required to design Economisers include

  1. Hot gas flow, pressure, temperature and nature of gas
  2. Feed water, temperature, pressure and flow
  3. Plain tube Economiser and ii) Extended surface Economizers

Plain tube Economisers and Extended surface Economisers

Plain tube Economiser

Plain tube Economiser is also known as Bare tube Economiser or Straight tube Economiser or inline Economiser or cross flow economizer. The most common and reliable economizer design is plain tubes in order to minimize ash fouling in solid biomass boilers and recovery boilers. Baretube Economisers are also very easy to clean with Soot blowers. Plain tube Condensing economizers are designed to accommodate the corrosive fluids generated when condensing the moisture out of the flue gas. Plain tube Economisers can raise the overall boiler efficiency by 8% to 10%. When coal is fired, the fly ash creates a highly fouled and erosive environment. The plain tube, inline arrangement minimizes the likelihood of erosion and trapping the ash as compared to a staggered arrangement.

Extended Surface Economisers

Extended Surface Economisers are also known as Finned type Economisers. Finned economizers are commonly applied in Gas-fired boilers and heat recovery steam generators (HRSG). Finned type non-condensing economizers are designed to maintain the flue gas temperature above the flue gas condensing temperature to prevent corrosion of the flue gas ducting. Fuels containing sulphur raise the overall flue gas dew point and when condensation occurs will lead to the formation of sulphuric acid‚ which is highly corrosive. Finned, the non-condensing economizer will raise the overall efficiency by 2% to 4%. Fin types enhance the heat transfer rate in the flue gas side, the fins are not subject to high pressure. So, for high-pressure applications, Finned type Economisers cannot be used. Finned tubes economizers can be either spiral or long finned. But Spiral Economisers is not recommended due to the possibility of multiphase erosion, flue gas washing, and sulfurous acid corrosion. with the following details for techno- commercial offer
Plain tube/ finned tube
Hot gas flow, pressure, temperature and nature of gas
Feed water, temperature, pressure and flow