WO2009083986A2

WO2009083986A2 - Method and system for generating energy with gas

Info

Publication number: WO2009083986A2
Application number: PCT/IL2009/000004
Authority: WO
Inventors: Yossi Ram
Original assignee: C.Cogen
Priority date: 2008-01-03
Filing date: 2009-01-01
Publication date: 2009-07-09
Also published as: EP2240667A2; IL188585A0; WO2009083986A3

Abstract

The invention relates to a system and a method for generating energy by the use of natural gas-operated energy-generating plant, capable of meeting different energy demand needs.

Description

METHOD AND SYSTEM FOR GENERATING ENERGY WITH GAS

FIELD OF THE INVENTION

This invention relates to a method and system for generating energy, in particular electricity, by natural gas.

BACKGROUND OF THE INVENTION

Electric power production and distribution networks need to respond to power demand that varies over time. The demand pattern has a daily, weekly and annual cycles and the electric power production needs to have a generation capacity to meet peak demands. It is clear that the value of the generated electric power is highest at times of peak demand, for example at early evening hours, at times of extreme heat or cold wave, etc.

Since electricity is a commodity that cannot be stored in its raw form, an electric power generating system has to be engineered for capacities to meet peak power demands. In particular, the fuel supply system for power plants needs to be designed to be able to supply the large amount of fuel needed to power the plant at such times.

The use of gas for fueling power stations is increasing. Natural gas is typically transported through pipes to sites in which it is utilized, such as a power plant. The common practice, in natural gas-operated power stations, is to feed the gas directly to the generators to power the plant. The amount of natural gas that can be fed into a power plant is of course dependent on the transport capacity of the supply pipe, which is in turn limited primarily by the pipe's diameter (a gas flow can of course be increased by increasing pressure, but supply pipes typically work within a certain defined working pressure range of about 60-80 bars). Thus, in order to be able to provide for high rates of fuel supply to meet peak electric energy demand, the pipe needs to have a sufficient diameter therefor. This factor, as can be appreciated, increases the complexity as well as the costs of the supply system. SUMMARY OF THE INVENTION

The present invention provides a method and system for generating energy from natural gas supplied through a gas piping system. The method and system of the invention permit to match the rate of gas feed to an energy-generating plant to meet different energy demand needs. In particular, the system permits an increase in the rate of gas feed at times of peak energy demand. The ability to increase the rate of gas feed to an energy-generating station is done, in accordance with the invention, without a need to design a piping system adapted to supply gas at a rate to meet peak demands. Rather, according to the invention an auxiliary, compressed natural gas (CNG) system is provided. At times other than times of peak demand, gas from the gas piping system is fed to the auxiliary gas supply system, is compressed and the CNG is then stored until need. At times of peak demand, gas to the energy-generating plant may be fed from said auxiliary system, instead of or in addition to gas fed directly from the piping system.

A preferred, albeit a non-exclusive type of energy generating in accordance with the present invention is electric energy.

According to one aspect of the invention there is provided a method for generating energy by a natural gas-operated energy-generating plant. According to the method of the invention an auxiliary CNG supply system is provided that comprises: (i) high pressure gas compressors units (for compressing the gas supplied by the gas piping system, typically having a pressure of about 60-80 bar, up to a relatively high storage pressure of about 250 bars) (ii) a high pressure gas storage subsystem, (iii) a gas feed linked to said supply piping system and adapted to feed compressed gas into said storage subsystem, (iv) an auxiliary piping system for feeding gas from the storage sub-system to the energy-generating unit, and (v) a valving subsystem to control gas feed from the gas storage sub-system to the auxiliary piping system. At times of peak energy demand, the valving subsystem is operated to supply gas from the auxiliary gas system to the energy- generating unit to power the said unit. Typically, at times of such peak demand, the energy generating unit is fed with the gas piping system and from the auxiliary CNG supply system, concomitantly. By another aspect the present invention provides a system for generating energy by the use of natural gas-operated energy-generating plant. The energy-generating plant is fed by a natural gas-piping system that transports gas from a gas source. The system comprises an auxiliary CNG supply system that comprises (i) high pressure gas compressor unit (ii) a high pressure gas storage subsystem, (iii) a gas feed linked to said supply piping system and adapted to feed compressed gas into said storage subsystem, (iv) an auxiliary piping system for feeding gas from the storage sub-system to the energy- generating unit, and (v) a valving subsystem to control gas feed from the gas storage subsystem to the auxiliary piping system. A control module is included for operating the valving subsystem to supply gas from the auxiliary gas system to the energy-generating unit at times of peak energy demand.

In addition to being able to provide auxiliary gas supply to permit a total gas supply at times of peak demands, the auxiliary CNG supply system also permits a limited back-up for supply of gas to the power plant at times where the natural gas piping system is malfunctioning.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the invention and to see how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawing, in which:

Fig. 1 is a block diagram of a system in accordance with the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

In the following, the system components are referred to each in the singular. It should, however, be understood that it is meant to refer also to a system with two or a plurality of such components. For example, the gas supply line may in fact be comprised of a number of such lines or pipes. The term "line" in this regards refers to a functionality of transporting gas through one or more pipes than a single component. Similarly, the ingress and egress gas lines may each include one, two or a plurality of pipes. Also, there may be one or more storage sub-systems, flow controllers, valves, etc. Reference is made to Fig. 1, showing a schematic depiction of a system in accordance with an embodiment of the invention. The system generally designated 100 includes a piping system 102 that transports natural gas from a gas source (not shown) and feeds the gas to the energy-generating plant, in this case an electricity-generating power plant 104. The plant includes one or more turbines (or engines). As generally known in the art, the natural gas can be fed directly from the piping system 102 to the gas power plant 104, typically through a filter system 108, a metering system 110 and a pressure regulating system 112 of one or more a gas supply lines 106.

In the piping system 102, natural gas is transported, typically at a pressure in the range of between about 60 to 90 bar. The natural gas is fed into the filter system 108 which filters out particulate matter and condensate liquid, typically via a separator in a one or two-stage design, which is known per se. As known, the separator condensate can be collected, stored in vessels and then transported away, e.g. by trucks and disposed.

The metering system 110 serves to gauge the amount of utilized natural gas. The design of metering system 110 depends, as known, on the energy-generating capacity of the electric power generating plant 104, or in other words on the intended natural gas flow rate. The design of a metering system is generally known per se and need not be elaborated herein.

The regulating system 112 serves for reducing the gas pressure from the supply pressure, typically in the range of between about 60 to 90 bar, to a lower pressure, typically in the range of between about 0.5 to 40 bar in which the natural gas is supplied to the turbines\ engines of the power plant 104. As known, the regulating system 112 may also include a gas preheating arrangement, which may, for example be gas/water pre- heaters known per se. The pressure regulated and optionally preheated gas is then fed to power plant 104 through the gas supply line 106.

Provided in accordance with the invention is an auxiliary gas supply system 120. It includes an ingress control valve situated on an ingress gas line 124 and an egress control valve 126 on egress gas line 128 for feeding gas from the auxiliary CNG supply system to the power plant 104. Valves 122 and 126 are typically motor-operated valves. The auxiliary CNG supply system 120 also includes a compressor 130, a CNG storage sub-system 132, a regulating system 133, a flow controller 134 and a system control unit 136.

The compressor 130 functions to compress the natural gas from its supply pressure, typically in the range of between about 60 to about 90 bar, to a higher pressure, usually in the range of between about 100 to about, 300 bar, typically above 200 bar. The compressor may be water cooled. The compressor may be associated with a gas filtering unit (not shown) for filtering liquid and particulate matter.

The storage sub-system 132 may include one or more or even a bank of storage tanks for storing high pressure CNG. The CNG storage capacity of the storage subsystem 132 is designed so as to be able to provide gas in access to that provided through supply lime 106 so as to provide sufficient gas to power plant 104 at times of peak demand. As will also be explained further bellow, at times of peak electric power demand gas may be fed to power plant 104 jointly from supply line 106 and from auxiliary gas supply system 120 (through egress gas lines 128). Where the storage sub-system 132 includes more than one tank, their use may be modular to modulate the amount of stored CNG. For example, at times when peak demand for electric power may be expected, e.g. in peak summer or peak winter, all tanks may be used to their full capacity. At other times, only part of the tanks may be used.

In addition to being able to support energy demands and hence peak gas supply demands, the auxiliary CNG supply system can also serve as an emergency back-up for use at such times where natural gas supply through the piping system is interrupted.

The regulating system 133 serves for reducing the CNG pressure, which is typically in the range of between about 100 to 300 bar, to a lower pressure, typically in the range of between about 0.5 to 40 bar. As known, the regulating system 133 may also include a gas preheating arrangement, which may, for example be gas/water pre-heaters known per se.

The operation of the system is controlled by control module 136, which is coupled to flow meter 138 that measures the amount of gas flow into line 106 through regulating systems 112 and 133, to flow controller 134, to valves 122 and 126 and to compressor 130.

At times of relatively low electric power demand, e.g. at night, the control module opens valve 122 and induces operation of compressor 130 to thereby store high pressure compressed natural gas (CNG ) in storage sub-system 132. This is in parallel to ongoing gas feed directly from piping system 102 through feed line 106 to power plant 104. At such, storage operation mode, valve 126 is usually closed.

Once electric power demand increases, control module switches system 120 into an auxiliary gas supply mode in which valve 126 opens and flow controller is activated to supply gas to plant 104 through gas egress line 128. In a typical auxiliary CNG supply operational mode, gas is supplied to power plant 104 both directly from piping system 102 through line 106 as well as from auxiliary CNG supply system 120 via line 128. It is also possible, by some embodiments to feed gas to power plant 104 during the auxiliary CNG supply operational mode only from the auxiliary gas supply system. This may be the case, for example, at times of interruptions in gas supply from piping system 102.

During auxiliary gas supply operational mode, in which gas is supplied to power plant 104 both directly from piping system 102 and from auxiliary supply system 120, control module 136 controls flow controller 134 so as to match the amount of gas supplied by the auxiliary supply system and the gas pressure, to that egressing from regulating systems 112 and 133.

Claims

CLAIMS:

1. A method for generating energy by the use of natural gas-operated energy- generating plant, comprising:

(a) powering the energy-generating unit by gas supplied directly from a piping system that transports natural gas from a gas source and feeds the gas to the energy-generating unit;

(b) providing an auxiliary compressed natural gas (CNG) supply system that comprises (i) a high pressure gas compressors units, (ii) a gas storage subsystem, (iii) a gas feed linked to said supply piping system and adapted to feed compressed gas into said storage subsystem, (iv) an auxiliary piping system for feeding gas from the storage sub-system to the energy-generating unit, and (v) a valving subsystem to control gas feed from the gas storage sub-system to the auxiliary piping system; and

(c) at times of peak energy demand, operating the valving subsystem to supply gas from the auxiliary CNG system to the energy-generating unit to power the said unit.

2. A method according to claim 1, wherein said energy is electric energy and said energy-generating unit comprises one or more gas-operated turbines or engines.

3. A method according to claim 1 or 2, wherein the gas feed comprises a compressor for compressing the gas fed into the CNG storage subsystem.

4. A method according to any one of claims 1-3, wherein at times of peak energy demand feeding gas to the energy-generating unit concomitantly from the gas supply piping system and from the auxiliary CNG supply system.

5. A system for generating energy by the use of natural gas-operated energy- generating plant, comprising:

(a) a piping system that transports natural gas from a gas source and feeds the gas directly to the energy-generating unit; (b) an auxiliary CNG supply system that comprises (i) a high pressure gas compressors units, (ii) a gas storage subsystem, (ii) a gas feed linked to said supply piping system and adapted to feed compressed gas into said storage subsystem, (iii) an auxiliary piping system for feeding gas from the storage sub-system to the energy-generating unit, and (iv) a valving subsystem to control gas feed from the gas storage sub-system to the auxiliary piping system; and

(c) a control module for operating the valving subsystem to supply gas from the auxiliary gas system to the energy-generating unit at times of peak energy demand.

6. A system according to claim 5, wherein said energy is electric energy and said energy-generating unit comprises one or more gas-operated turbines or engines.

7. A system according to claim 5 or 6, wherein the gas feed comprises a compressor for compressing the gas fed into the gas storage subsystem.

8. A system according to any one of claims 5-7, adapted for feeding gas to the energy generating unit concomitantly from the gas supply piping system and from the auxiliary supply system.