GB2055628A - Apparatus for removing impurities from gases - Google Patents

Abstract

Apparatus for removing impurities from a gas comprises in flow series an electrostatic separator (14) which receives contaminated gas from a coal burning fluidised bed combustor (10). The partially cleansed gas flows from the separator (14) to a pair of cyclone separators (20, 21) connected together in series. The clean air produced is to drive a gas turbine (23). <IMAGE>

Description

SPECIFICATION Electrostatic filters This invention relates to apparatus for removing impurities from gases.

It is frequently necessary to clean large volumes of gas. The vent stocks for industrial and chemical process plants are one area where this is necessary and another such necessity arises in the cleaning of exhaust gas from a coal firing burner which is to be used to power a gas turbine.

The types of impurity in the gas may include relatively large particles of ash or the like but also include much smaller particles such as aerosols of sodium and potassium which are particularly found to be present in the coal burning exhaust gas referred to above. It is normal practice to remove particles by a centrifugal separation method and to remove the smaller aerosols using an electrostatic precipitator or the like. However, it has been found to be difficult to arrange for removal of the collected aerosols from the electro-static device.

The present invention provides an apparatus in which the presence of the life particles is itself used to assist continuous cleaning of the electro-static device.

According to the present invention apparatus for removing impurities from a gas comprises an electro-static separator in which both large and small particles are simultaneously removed from the gas followed by a centrifugal separator connected in series with the electro-static device.

In this way the small aerosol particles are caused to adhere to the larger particles and then may be removed from the electro-static device by vibration or simply by gas flow to be connected in the centrifugal separator.

The invention will now be particularly described merely by way of example with reference to the accompanying drawing which shows a coal burning gas turbine arrangement using apparatus in accordance with the present invention.

In the diagram there is shown a fluidised bed combustion system 10 which is fed with pulverised coal from a hopper 11. Air for the combustion of a coal enters the bed through an intake 1 2. The exhaust gas from the fluidised bed leaves through a duct 1 3. It will be appreciated that the exhaust gas will include a significant proportion of impurities. In particular there are particles of sodium and potassium at a level of approximately one part per mile by weight and having particle sizes in the range 0.1-1 microns. In addition there will be a proportion of relatively larger particles of ash of 2-50 microns in size.

In order to remove these impurities from the gas an electro-static separator 1 4 is provided. In the separator the gas passes in between wires 1 5 which are charged by a duct 1 6 to a high negative electro-static potential relative to surrounding plates or tubes.

The particles of ash together with the aerosol sodium and potassium particles are attracted away from the wires and stick to the plates.

Because of the presence of the relatively large particles of ash the aerosol particles are more likely to adhere to the ash particles rather than to the plates themselves. They can therefore be removed from the plates by a simple technique such as vibration of the plates or even by this scrubbing effect of the gas stream.

In the diagram the separator 14 is shown to have a sloping floor 1 7 which would direct particles which have fallen from the plates to a waste outlet 18.

Exhaust gas from the separator 14 then flows through a duct 1 9 to a pair of conventional cyclone separators 20 and 21 mounted in flow series. In these separators the remaining ash particles which are likely to be present in quantities too great to be dealt with by the electro-static duct, are removed. The clean air thus produced passes through an outlet duct 22 to drive a gas turbine 23 whose output at shaft 24 will be used to drive any form of load.

It will be understood that in effect the apparatus of the invention reverses the normal sequence of centrifugal separator and electrostatic separator. In this way the eleetro-static device is enabled to be self cleaning in operation when used with very small particles which would otherwise be difficult to remove.

1. Apparatus for removing impurities from a gas comprising a electrostatic separator in which both large and small particles are simultaneously removed from a gas by a centrifugal separator connected in series with the electrostatic separator.

2. Apparatus for removing impurities from a gas constructed and arranged for use and operation substantially as herein described, and with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (2)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Electrostatic filters This invention relates to apparatus for removing impurities from gases. It is frequently necessary to clean large volumes of gas. The vent stocks for industrial and chemical process plants are one area where this is necessary and another such necessity arises in the cleaning of exhaust gas from a coal firing burner which is to be used to power a gas turbine. The types of impurity in the gas may include relatively large particles of ash or the like but also include much smaller particles such as aerosols of sodium and potassium which are particularly found to be present in the coal burning exhaust gas referred to above. It is normal practice to remove particles by a centrifugal separation method and to remove the smaller aerosols using an electrostatic precipitator or the like. However, it has been found to be difficult to arrange for removal of the collected aerosols from the electro-static device. The present invention provides an apparatus in which the presence of the life particles is itself used to assist continuous cleaning of the electro-static device. According to the present invention apparatus for removing impurities from a gas comprises an electro-static separator in which both large and small particles are simultaneously removed from the gas followed by a centrifugal separator connected in series with the electro-static device. In this way the small aerosol particles are caused to adhere to the larger particles and then may be removed from the electro-static device by vibration or simply by gas flow to be connected in the centrifugal separator. The invention will now be particularly described merely by way of example with reference to the accompanying drawing which shows a coal burning gas turbine arrangement using apparatus in accordance with the present invention. In the diagram there is shown a fluidised bed combustion system 10 which is fed with pulverised coal from a hopper 11. Air for the combustion of a coal enters the bed through an intake 1 2. The exhaust gas from the fluidised bed leaves through a duct 1 3. It will be appreciated that the exhaust gas will include a significant proportion of impurities. In particular there are particles of sodium and potassium at a level of approximately one part per mile by weight and having particle sizes in the range 0.1-1 microns. In addition there will be a proportion of relatively larger particles of ash of 2-50 microns in size. In order to remove these impurities from the gas an electro-static separator 1 4 is provided. In the separator the gas passes in between wires 1 5 which are charged by a duct 1 6 to a high negative electro-static potential relative to surrounding plates or tubes. The particles of ash together with the aerosol sodium and potassium particles are attracted away from the wires and stick to the plates. Because of the presence of the relatively large particles of ash the aerosol particles are more likely to adhere to the ash particles rather than to the plates themselves. They can therefore be removed from the plates by a simple technique such as vibration of the plates or even by this scrubbing effect of the gas stream. In the diagram the separator 14 is shown to have a sloping floor 1 7 which would direct particles which have fallen from the plates to a waste outlet 18. Exhaust gas from the separator 14 then flows through a duct 1 9 to a pair of conventional cyclone separators 20 and 21 mounted in flow series. In these separators the remaining ash particles which are likely to be present in quantities too great to be dealt with by the electro-static duct, are removed. The clean air thus produced passes through an outlet duct 22 to drive a gas turbine 23 whose output at shaft 24 will be used to drive any form of load. It will be understood that in effect the apparatus of the invention reverses the normal sequence of centrifugal separator and electrostatic separator. In this way the eleetro-static device is enabled to be self cleaning in operation when used with very small particles which would otherwise be difficult to remove. CLAIMS

1. Apparatus for removing impurities from a gas comprising a electrostatic separator in which both large and small particles are simultaneously removed from a gas by a centrifugal separator connected in series with the electrostatic separator.

2. Apparatus for removing impurities from a gas constructed and arranged for use and operation substantially as herein described, and with reference to the accompanying drawings.