GB2446595A

GB2446595A - A gas turbine power plant operating on flare gas

Info

Publication number: GB2446595A
Application number: GB0702794A
Authority: GB
Inventors: Peter John Lo
Original assignee: Individual
Current assignee: Individual
Priority date: 2007-02-14
Filing date: 2007-02-14
Publication date: 2008-08-20
Also published as: GB0702794D0

Abstract

The invention entails a gas turbine power plant Q which is fuelled with flare gas. The flare gas is preferably obtained from an oil refinery (A), where instead of being burnt as waste gas in a flare stack, is channelled to a simple or combined cycle AB gas turbine power plant Q. Preferably, the flare gas is blended with natural gas before being supplied P to combustor of the gas turbine power plant which in turn drives a generator R to provide electrical power. Ideally, there are chromatograph and contaminant analysers K1, K2 to check the quality of the flare gas, which may divert the gas to a heat recovery steam generator supplementary firing system (AA) if it is not of sufficient quality for the gas turbine Q. Flare gas of low quality may be burnt in the flare stack Z. The gas turbine power station is preferably located near an oil refinery.

Description

--2446595 Title: Efficient Pre-Combustion Apparatus for use in Simple

or Combined Cycle Power Plants

Description

The operation of gas turbines in simple or combined cycle operation typically involves the reliance on a single fuel source which is mainly gas. For power projects that are located close to or can gain access to a source of flare gas, the flare gas can be used as a blend with the primary gas fuel and therefore reduce dependency on the primary fuel source, and if the flare gas is significantly cheaper than the primary fuel source, significantly reduce the variable cost of operating a power plant. At the same time, the refinery! other industry which supplies the flare gas is providing the flare gas for energy recovery rather than waste.

The flare gas line, with the contaminants required to be removed under the power plant operating license! environmental permit, would initially comprise a tee off line from the flare gas supply line from the refinery at A. The line would have a gas chromatograph and gas analyser fitted to it at Ki. If Ki goes out of gas specification for the gas turbine at 0 and the heat recovery steam generator supplementary firing at AA (if this exists) this valve Gi closes and the flare gas is bypassed and returned to the refinery at Z for traditional flare burning. Q and AA (if exists) are supplied entirely by their primary gas source, S. If Ki is within gas specification for Q the valve 01 remains open, valve G3 is closed and valves 02 are open to allow all of the flare gas to be used in the gas turbine, as this would be a more efficient use of the flare gas if it is a combined cycle plant. If Ki is within gas specification for AA (if this exists) but not for Q, valve 01 remains open, valves G2 are closed and valve G3 is opened to allow the flare gas to be used in AA. Whilst this is less efficient than use in a gas turbine in combined cycle operation it maximises the use of the flare gas which would otherwise be bypassed back to the refinery/ source of flare gas. After Gi the flare gas feeds into a gas compressor at C located near to the power plant site (in which case auxiliary power and backup power could come from the power plant) or alternatively adjacent to the refinery if space is limited (in which case auxiliary power and backup power could come from the refinery). The flare gas pressure just after C would be boosted to a supply pressure greater than the supply pressure of the natural gas at the mixing point where the two gases blend, and take into account the pressure loss of the system. Flame arrestors would be included at appropriate intervals along the line (not shown but in line with good engineering practice) as well as emergency slam shut valves D and N. The flare gas would pass through a filter separator and drain tank arrangement at E and F. The final let down of the flare gas into the natural gas stream would be controlled via control valves 02 whose operation would be function of: 1. Flare gas properties from the energy flow computer at X and chromatograph Ki and K2 including heating value 2. Natural gas properties from the energy flow computer at U and natural gas chromatograph including heating value 3. Blended gas properties from the integrated energy flow computer at W and chromatograph at K3 including heating value 4. Natural gas supply pressure at mixing point measured through pressure transmitter at AB 5. Gas turbine operating mode (start, shutdown, provision of frequency response), trip or alarm feedback (pulsations, humming, exhaust temperature spread, flame instability etc) feed back from plant OCS at V which would cause the flare gas stream to be shut down at valves Gi, D, G2, G3 and N. The natural gas supply line with take over for 100% of the power plant supply requirements at S. The emergency slam shut valves operation would be a function of: 1. Natural gas line emergency slam shut valves 2. Gas turbine trip! breach of pre-determined alarm levels to enable early acticn to be taken and the gas supply to switch to 100% primary gas feed under existing control logic for primary gas supply 3. Operation of flame arrestors After G2 the flare gas would pass through temperature measurement at H and pressure measurement at I. Flow would be measured at a calibrated orifice plate at J. After J the flare gas is connected to a gas chromatograph and analyser at K2 which checks the gas specification and heating value for energy calculation purposes. (Ki purpose is used for valve positioning purposes at GI, G2, G3) L is an emergency vent used during times when the emergency shutdown valves at D and N are used to bring the flare gas pipeline down to atmospheric pressure prior to purging through purge valves M, if required.

After N the flare gas passes through flow straighteners into an in line mixing tee at 0 where it is blended with the primary gas source, S. At this point samples of the blended gas are taken in a gas chromatograph/ gas analyser to check the quality of the blended gas. The blended gas then enters the gas turbine for combustion at P and generation of electricity at generator R. Option 1 is shown as the broken dotted line around AA and valve G3 and associated pipework teeing off between E and G2.

Option 2 is shown as the broken dotted line around as AB, the combined cycle apparatus additional to the simple cycle gas turbine arrangement.

Control cabling is shown as the dotted line. Pipe work is shown as the solid line.

Title: Efficient Pre-Combustion Apparatus for use in Simple or Combined Cycle Power Plants Drawings -Sheet 2 of 2 Legend for Figure 1: A Flare gas from refinery! other source with contaminants removed B Flare gas compressor _________________________________ C Purge valve D Emergency shutdown valve E Filter separator F Filterdrain tank Gi Fail close bypass valve.

G2 Control valves for pressure let down purposes G3 Control valve to let flare gas enter the heat recovery steam generator __________ supplementary firing (if this exists) H Temperature element used as input to the corrected flow! energy flow _________ calculations Pressure transmitter used as input to the corrected flow! energy flow __________ calculations J Calibrated orifice Plate for flow measurement Ki Gas Chromatograph and Contaminant Analyser for flare gas routing purposes, controls positions of valves GI, G2, G3 to divert flare gas back to refinery, divert flare to gas turbine only, divert flare to HRSG _________ supplementary firing only (if this exists) respectively K2 Gas Chromatograph and Contaminant Analyser for flare gas energy flow _________ calculation purposes L Emergency gas vent M Purge valves N Emergency shutdown valve 0 In line mixing tee with flow straighteners P Blended fuel in (flare gas and natural! primary gas) Q Gas turbine R Generator S Natural! primary gas in T Natural! primary gas reducing and metering skid (details not shown) U Natural! primary gas flow and energy computer V Signals from power Plant: Gas Turbine Trip, Flame Instability, Predetermined alarms that shut down control valves and/ or emergency _________ shutdown valves W Blended gas flow and energy computer X Flare gas flow and energy computer Y Distributed control system Z Flare gas return line when Ki goes out of gas specification for Q and AA AA Heat recovery steam generator supplementary firing (if this exists) - _________ Option 1 AB Combined Cycle Block -Option 2

Claims

-L

Title: Efficient Pre-Combustion Apparatus for use in Simple or Combined Cycle Power Plants Claims 1. Allows the use of flare gas in a blend with the primary gas supply in the combustor of the gas turbine.
2. The application is for use in combined cycle gas turbine power plants.
3. The application is for use in simple cycle gas turbine power plants.
4. The application is for use in gas turbines of greater than 1 MW installed capacity and, for example, include but not limited to E, F, G and H class gas turbines.
5. The project is environmentally friendly as the burning of flare gases would be for energy recovery instead of waste emissions to atmosphere.
6. The apparatus promotes sustainable development.
7. The apparatus promotes corporate social responsibility.
8. The apparatus uses proven technology (flare gas compressor, flame arrestors, pipe, controls valves, emergency shutdown valves, chromatograph, orifice plate, temperature element, pressure transmitter, control cabling, control logic, in line mixer tee, purge valves, filter separators. filter drains tank, energy flow computers for the flare gas stream, primary gas supply stream and blended streams)
9. The apparatus is scalable.
10. The apparatus can be customised according to the blending ratios required.
11. The apparatus can be customised to the composition of the flare gas used.
12. The apparatus can be customised to the requirements of the specific gas turbine used.
13. The apparatus can be customised to the requirements of the specific heat recovery steam generator used (if this exists).
14. The combustion of the blended gas takes place at the gas turbine and therefore in combined cycle operation mode the efficiency will be much higher than use of flare gas in supplementary firing in heat recovery steam generators.
15. The combustion of the blended gas takes place at the gas turbine and therefore in simple cycle operation mode reduces reliance on the primary fuel.
16. The combustion of the blended gas takes place at the gas turbine and therefore in combined cycle operation mode reduces reliance on the primary fuel.
17. The project remains stable during start-up, shutdown or provision of frequency response to the high voltage grid as the controls can be customised to switch off the flare gas supply during these periods of transient operation, if required and allow the power plant to rely 100% on the primary fuel source.
18. The flare gas may be bypassed to the heat recovery steam generator supplementary firing (if this exists) if the gas specification is outside of the gas turbine requirements but within the heat recovery steam generator supplementary firing requirements (if supplementary firing exists) and therefore maximises the use of the flare gas.
19. The flare gas may be bypassed entirely back to the refinery if the gas specification is outside of the gas turbine and heat recovery steam generator supplementary firing (if this exists) and burned in the traditional manner.
20. In scenario 12 the gas turbine and heat recovery steam generator supplementary firing (if this exists) is fed entirely from the primary gas source to maintain security of supply.