Objective To install and test a top gas pressure relief turbine to use the pressure drop in the blast furnace after waste gas cleaning to generate electrical power (13,480 kW) to achieve annual energy saving of 7,760 TOE at project level. Assuming average power plant efficiency, this should correspond to primary energy saving of +- 27,000 TOE/y.To perform the test programme, 60 measuring points were logged. An electronic digital measuring point logging system was also put into operation in parallel with the conventional analogue one. Most of these measuring points were equipped with a buffer amplifier to prevent signal interference.The turbine output depends primarily on pressure drop, inlet temperature and mass flux ie. on factors influenced by the operational mode of up and down stream facilities.In order to take account of these variables, the following influencing parameters were examined:- increasing inlet pressure;- reducing outlet pressure;- increasing gas inlet temperature;- reducing scrubber water temperature;- gas flow rate;- top gas composition.A total of three main trials and preliminary tests were conducted between April and August 1983.To attain the greatest possible output, not only from the turbine facility but the entire system of blast furnace, gas purification turbine and BF gas distributionnetwork had to be optimised in terms of interaction.As a result of pre-heating in the cowper, blast volume increases approximately threefold and is converted into top gas in the blast furnace, occupying +/- 60% more space than the cold blast at the top of the furnace, at 100-150 deg.C.A pressure increase upstream of the scrubbers was mixed by reducing pressure loss within the Venturi scrubbers. Three annular gap bodies installed in each of the two scrubbers mix gas and water. Inlet pressure was raised by increasing the pressure lost at the annular gaps by +/- 60 Mbar, yielding a gain of 240 kW.Increasing compressor pressure by 100 Mbar would result in +/- 500 kWh additional power consumption, of which +/- 350 kWh is recoverable by the turbine.From the operational point of view, scrubber water volume reduction presents a problem. The risk of caked-on dust deposits could be reduced by installation of an additional pinstock in the dome of the scrubbers. Another long-term investigation will be necessary to achieve water system consistancy, to provide information on parameter values.An increase in output of 240 kWh (2%) appears to be possible on the turbine, and an additional 40 kWh could be saved as a result of reduced pump capacity, yielding an estimated gain of 220,000 DM.A study of the various influences exerted on the turbine output was undertaken, not only by measurements and computations, but by a cost-efficiency analysis, to measure achievable gains and to show how practical the influences for increasing turbine output are.Top-gas pressure allows appreciably higher specific outputs for a given furnace volume. Longer gas residence time in the blast furnace leads top gas flow homogenisation and reduced coke consumption. While a low fraction of gas pressure (0.25 Bar max.) is required for the downstream gas cleaning system, residual pressure 2 Bar max. is lost through throttling, equivalent to +- 30% of energy used for blast compression.In order to utilize the pressure drop in the top gas after waste gas cleaning it was decided to install a pressure recovery turbine which is located downstream of the scrubbers in the already existing gas purification facilities at Schwelgern.It was decided to install a double-flow, four stage axial type reaction turbine designed to generate 13.5 MWh from a gas throughput of 587,000 m3/h, admission temperature of 45 deg C and a differential pressure of 1.8 Bar. The cast steel turbine casing is 3,870 mm in length, 3,500 mm maximum height. The rotor is 6,055 mm long, of1,692 mm maximum diameter and weighs 75 Tons. The admission guide blades of the first stage are variable to attain a regular top-gas pressure. In addition, they ensure identical efficiency over a broad operating range.Coupled to the turbine is a 14 MWh self-excited asynchronous generator of 1,500 rpm output speed. When switching to the power network, the self-excitation mode precludes any voltage drop. By connecting capacitors to the generator terminals, cover for the no-load reactive power is guaranteed. Gas pressure within the network is 0.2 Bar. All operational sequences are predetermined, executed and monitored by a control and regulating system. Turbine start-up and shut-down is automatic with no appreciable effect on top gas pressure.Licences can be obtained from Zimmermann & Jansen. Programme(s) ENG-ENALT 1C - Programme (EEC) of financial support for projects to exploit alternative energy sources, 1979-1984 Topic(s) 1.6 - INDUSTRY Call for proposal Data not available Funding Scheme DEM - Demonstration contracts Coordinator Thyssen Stahl AG EU contribution No data Address Kaiser-Wilhelm-Straße 100 47057 Duisburg Germany See on map Total cost No data
