Power and performance of TRT parameters and functions

TRT parameters:

• Volume of BF top gas

• Pressure of BF gas at the blast furnace top

• Pressure drop across the gas cleaning plant (GCP)

• Temperature of BF gas after the GCP

• Pressure of BF gas at the outlet of the TRT

• Quality of the BF gas at the blast furnace top

• Efficiency of TRT

• Efficiency of the generator coupled with the TRT 

Top gas from blast furnaces typically has a dust content of around 5 g/N and is passed through a gas cleaning plant (GCP) to reduce the dust content to below 5 mg/N.Reduction of the dust content is necessary for the proper operation of the TRT.

BF top gas systems with TRT units are divided into wet and dry gas cleaning systems,depending on the method they are used to remove dust particles.Dry systems use less water and electricity.They have a lower pressure drop and about 50°C higher gas temperature than wet systems.With dry gas cleaning,TRT systems can typically produce 30% more power and have the potential to produce up to 60% more power.Therefore,dry systems are considered to have more favorable economics.There are two types of turbines:radial and axial.At present,the axial flow turbine is widely used in TRT because it is more suitable for handling large flows.TRTs are typically multi-stage variable expansion turbines of axial reaction design,typically with a horizontally split casing and a governor speed of 3,000 rpm.TRT generally uses a brushless excitation synchronous generator.Generators are usually designed to operate under all the load conditions imposed by the turbines to which they are connected.TRT generators typically generate 6.6 kV,which is then stepped up to 33 kV by a 6.6kV/33 kV step-up transformer.The stability of the top pressure is critical.The pressure fluctuation on the top of the furnace is small,which is beneficial to the operation of the blast furnace.According to the increase or decrease of the blast furnace gas volume, the top pressure is controlled by opening or closing the first-stage stator vane of the steam turbine.For conventional steam turbines,a governor valve is also used in combination to control the top pressure.However,the regulating valve causes a larger pressure loss than the stator vane,and thus is disadvantageous in terms of power recovery and noise prevention.

Therefore,in the system that is widely used now,the speed control valve is canceled,and the top pressure is only controlled by the first-stage stator vane.After the dust is removed by the gas purification equipment,the clean blast furnace gas enters the steam turbine through the inlet butterfly valve and the inlet eye protection valve.Normally closed bypass valve and normally open emergency shut-off valve for emergency situations.In TRT,the mechanical work produced by the turbine is transferred to a generator to provide electricity.Low pressure,low temperature blast furnace gas enters the gas pipeline through the outlet eyepiece valve.The operation of TRT can be divided into two phases,namely (i) startup phase and (ii) normal operation phase.During the start-up phase,all preparations such as hydraulic subsystems must be checked.The signal to start the TRT is then sent to the BF operator.If the blast furnace operator agrees,open the water inlet butterfly valve and the emergency shut-off valve.The speed of the steam turbine is controlled by the imported butterfly valve,and the pressure of the top gas is controlled by the diaphragm valve.The diaphragm valve is slowly closed until the steam turbine reaches the required speed.The startup phase then transitions to the normal operation phase.During normal operation,the top gas pressure is completely regulated by the first-stage stator blades of the steam turbine.Top pressure is controlled by opening or closing the first stage stator vanes of the turbine.In cases where the required top gas pressure and top gas volume are not available, the gas can bypass the TRT.A closed high pressure eye mask valve provided in the circuit ensures uninterrupted operation of the blast furnace with complete isolation of the TRT, e.g.during maintenance phases.

The TRT system can be synchronized with the steel plant power distribution system. A TRT plant typically has the same availability as a blast furnace running 350 days a year. Auxiliary consumption of TRT power plants is very low.TRT is a proven technology and there is very little risk to its installation or operation.Should the TRT system fail for any reason,the expanded gas will be contained in the existing scrubber.This is normal in blast furnaces that do not have a TRT system installed.It has no effect on the operation of the blast furnace and does not consume blast furnace gas. Because BF gas is so flammable,it is often used in other parts of the plant to generate heat or energy for other processes.With a TRT system installed, the BF gas can effectively generate energy twice-once in the turbine and once when it is combusted normally.TRT is a cleaner and more energy-efficient technology because it utilizes the pressure energy in the process exhaust stream.TRT is used to save energy and reduce greenhouse gas emissions.While the economics of installing a TRT are considerable,environmental advantages are also an important consideration.TRT is very sustainable because the power generation process using this technology produces zero emissions.The process is 100% green.

TRT functions:

• Energy-saving technologies applied to blast furnaces in steel mills.

• Power generation equipment with blast furnace top pressure control.

• Use the blast furnace gas generated by the blast furnace to drive the turbine to generate electricity.

• Generate electricity without fuel.

• Since no fuel is burned, no carbon dioxide or other greenhouse gases are produced.

• The TRT system contributes to the reduction of CO2 emissions according to the amount of electricity generated.

• Compared to traditional diaphragm valves,the TRT system produces less noise,helping to improve the environment around the blast furnace.

• The operation and maintenance of the TRT system does not require complex technology,and can be easily completed by blast furnace operation and maintenance personnel.Only a small amount of water,nitrogen,etc.is required for operation,and can be easily covered by the existing equipment of the blast furnace.