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© Gießerei G. Siempelkamp GmbH & Co.KG
Dual fuel engine generates electricity from cupola furnace gas
Projektinfo 02/2012

Fig. 1: Schematic depiction of the cupola furnace process with the CFG engine.
© Betriebsforschungsinstitut BFI

Fig. 2: CFG test engine on the BFI test rig.
© Betriebsforschungsinstitut BFI
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Generating electricity and heat from lean gas

White-hot molten iron flows into the launder . The blast of heat released provides visitors with an impressive demonstration of the amount of energy flowing in foundries. Large volumes of carbon (coke) are used for the melting process in the cupola furnace, whereby a combustible process gas is formed as a by-product. This so-called cupola furnace gas has a low heating value and has previously been completely combusted for generating the hot blast in the cupola furnace’s recuperator. However, in this process only around 35 % of the contained energy is used thermally. Now it is possible to utilise the remaining 65 % of the chemically bound energy that was previously not used in most foundries: a modified biogas combined heat and power plant runs with cupola furnace gas (CFG) from the melting furnace.

Wolfgang Adler and Jörg Adam from Betriebsforschungsinstitut GmbH (BFI), who are two of the developers of the new system, explain: “Instead of wastefully burning off surplus, low-calorific process gas that cannot be used in the furnace operation, a newly developed dual fuel engine burns the cupola furnace gas. The generated electrical energy is used in the operation network while the thermal energy flows via the recuperator into the hot blast generation system for the melting furnace. The cogeneration (CHP) now enables an overall efficiency of 80 % to be achieved.”

The comprehensive utilisation of the entire cupola furnace gas in the factory is worthwhile since the energy costs and CO2 emissions sink and the cost-effectiveness improves. Until now, a total of approximately 3,000 TJ of energy from cupola furnace gas was previously insufficiently utilised in Germany each year when melting metal for producing cast iron in cupola and shaft furnaces, which is very energy-intensive.

Energy efficiency through cogeneration

In view of the insufficient utilisation of this energy, a plant for the combined generation of electricity and heat from cupola and blast furnace gas was developed and tested in operation for industrial use as part of a joint project with an iron foundry and a gas engine manufacturer. The most important goals of this research project were to reduce the energy consumption and CO2 emissions in the foundry operation while maintaining the reliability of the cupola furnace operation and the high quality of the cast products. The challenge for the researchers was in achieving the complete engine combustion of the very low-calorific process gas. The researchers successfully tested the CHP plant in a test rig and drew up concepts for incorporating it in various methods of operation for the cupola furnace.

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The dual fuel engine is now running smoothly

Until now, once the cupola furnace gas has been cleaned of dust and other impurities it is mostly burned in the recuperator (heat exchanger) and the released thermal energy is used for generating hot blast. With the newly developed system, the portion of the process gas that is not absolutely needed flows via a bypass into the CFG engine, which generates electrical energy and, with is exhaust gas, contributes to generating hot blast in the recuperator. The engine exhaust gas is then afterburned in the recuperator. The exhaust heat from the engine cooling system is used for pre-heating the combustion air for the recuperator. This means that the exhaust air is almost completely incorporated into the cupola furnace process.

If, for production reasons, there is a lack of process gas, the engine capacity can be reduced to partial loading or more pilot oil can be injected. Since the engine should be switched off as little as possible in order to extend its service life, continually operation of the cupola furnace is a prerequisite for the use of this innovative technology. At the Hüttenwerke Krupp Mannesmann (HKM) foundry in Duisburg, Germany, the dual fuel engine was integrated within a burner test facility belonging to the BFI. It was connected to the foundry’s gas network and operated with blast furnace gas (Fig. 2). The blast furnace gas at the Hüttenwerke foundry is very similar to cupola furnace gas and was suitably adapted for the field tests so that it accorded with the composition of conventional cupola furnace gas.

In various test series at the BFI’s burner test facility and at Schnell Motoren AG, the researchers were able to successively optimise the operation of the dual fuel engine with low-calorific process gases. An important aspect was to avoid sudden fluctuations in the heating value of the fuel gas, since otherwise local overheating of the cylinder head and exhaust gas system could damage the engine.

The investigations showed that the electrical efficiency of the dual fuel engine when operated with cupola furnace gas was between 35 and 40 %. Since the engine exhaust heat can be mostly recycled in the production process, the overall efficiency of the CHP plant increases to more than 80 %. The proportion of pilot oil (diesel, RME or vegetable oil) is less than 10 %. The further developed dual fuel engine achieves an electrical output of roughly 210 kW; it then uses almost 800 m³ of cupola furnace gas per hour.

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Development and testing
SCHNELL Motoren AG