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Exhaust air filtration & Energy recovery in foundries
Case study: Exhaust air filtration systems for foundries in comparison
The energy consumption in foundries is highly depended on the energy use of exhaust air and supply air systems. Higher energy consumption means high production costs and high CO2 emissions. As a full solution provider, KMA offers energy saving exhaust air filter for any application and thus enables considerable savings up to 85 %.
The overview includes the explanation of the possible solutions.
Calculation basis: Foundry in Central Europe, equipped with 10 die casting machines (1100 t) and a exhaust air volume of 80000 m3/h. Ø outdoor air temperature during heating period (3600 h): 2.9° C, desired hall temperature: 18° C (Δt = 15.1 °C).
Cost approach: gas price: 0.50 €; current price: 15.5 Cent/kWh.
Conventional exhaust air mode
The exhaust air is extracted by customized hoods above the machines and filtrated by means of a simple demister and carried outside by ventilators. Due to the simple filtration a transport of the emissions from inside to outside only takes place.
Especially in the cold winter months this simple process of discharging the exhaust air to the outside results in high follow-up costs, because the air exhausted into the atmosphere must be replaced by the same volume of fresh air and the heating of the cold outdoor air to room temperature leads to high operating costs and high CO2 emissions.
Operating costs: 152000 €
CO2 emission: 592 tonns
Here you can download the case study as pdf – published in the magazine Giesserei (11/2012)!
The extraction hoods are extended by high efficient filter systems with integrated heat exchanger. The filter system consists of demister, electrostatic filter cells and automatic filter cleaning system.
The electrostatic filter is particularly important in this case, because it permits the high-grade separation of oily and greasy emissions as smoke, dust and mist. This high efficient filter method not only helps avoiding environmental pollution, but also maintaining the efficiency of the heat exchanger permanently. The heat exchanger extracts heat from the warm exhaust air and transfers it to the incoming fresh air by direct combination.
Energy savings during the heating period: 625000 kW (= approx. – 73000 m3 gas/year). Deducting the energy consumption of the heat recovery system (circulation pump) from the saved energy volume results in
Reduction of the operating costs of about approx. 36000 € per year
Reduction of CO2 -emissions of about -141 tons per year
Amortization period of the system of about 2 years
KMA filter system incl. heat exchanger and heat pump
1. Smoke from die casting machine; 2. Centralized filter station: exhaust air is filtered. Subsequently, heat is extracted by a heat exchanger; 3. The filtered and cooled air is blown outdoors; 4. With the help of the heat pump heat water (40° C) is produced; 5. Fresh air is heated by a supply air heat exchanger and blown into the production hall.
Concept 2 is extended by a high efficient heat pump. Exhaust air pumps take their energy from the warm hall exhaust air and allow a direct energy transfer (without buffer) to the supply air to be heated. The resulting high coefficient of performance of more than 6 means, that 6 kW thermal energy is recovered from 1 kW electrical current.
Inspired by the high coefficient of performance and the increased efficiency the company recovers by using a KMA Exhaust Air Filtration System with integrated heat exchanger and heat pump almost twice as much energy as with the simple heat exchanger of concept 2.
Deducting the energy consumption of the filter system from the saved energy volume results in
Reduction of the operating costs of about approx. 53000 € per year
Reduction of CO2 -emissions of about -225 tons per year
Amortization period of the system of about 3 years
Decentralized KMA filter system in circulating air mode
Currently, the most energy efficient process of exhaust air treatment is the recirculating-air operation. Each single die casting machine is equipped with an KMA extraction hood and KMA filter system. Each exhaust air filtration system is equipped with demisters, electrostatic filter cells and automatic cleaning system, which ensures the regular filter cleaning.
The high-performance filter technology enables such a high clean air quality, that the filtered air at the filter outlet can be returned to the production hall. As the air circulates inside the hall there are no heat losses during the winter period due to the exchange with cold supply air. This method has the biggest savings potential and in addition to this, there is no need for costly exhaust air pipework.
Reduction of the operating costs of about approx. 97000 € per year
Reduction of CO2 -emissions of about -377 tons per year
Amortization period of the system less than 3 years
Depending on individual parameters (e.g. exhaust air volume, outdoor temperature) energy savings up to 80 % are possible.