The subject of the invention is the method of compensating fluctuations in gas demand in natural gas networks and the technological layout of the installation for compensating fluctuations in gas demand in natural gas networks by using energy-free compression-storage-expansion installation.

Natural gas is transported from the sources to places of use via network of medium and high pressure pipelines, usually working under pressure of 3 - 8 MPa. Generally prior to supplying gas to the end users, especially the municipal ones, the gas pressure must be reduced to less than 0.35 MPa. Therefore, network reduction stations are located at the transmission pipelines, where the gas pressure is reduced to the level required in the distribution networks.

Natural gas pipeline networks do not operate under steady-state conditions because gas demand changes both in hourly, daily, weekly and seasonal cycles related to summer - winter seasons. Such fluctuations in demand require compensation, because in extreme cases they can cause periodic gas shortages at customers.

Medium and high pressure pipelines are characterized by possibility of compensating fluctuations in gas demand resulting from operating at a certain level of pressure range, which makes it possible to store gas in an amount depending on the diameter and length of the pipeline and the allowable range of changes in the working pressure. These stored quantities are usually not sufficient to compensate for fluctuations in gas demand, which may result in periodic gas shortages, especially in the end zones of the pipelines, where large pressure drops may occur, preventing proper operation of the gas network.

The system known from the Polish patent description PL 198956 is the pipeline system of the gas distribution station with multidirectional power supply and distribution, which is equipped with shut-off and check valves and filtration units.

The Polish patent description of PL 203759 describes a piping system of the gas distribution station with multidirectional power supply and distribution, which thanks to equipping it with cross-flow pipelines solves the movement problems of the distribution station.

There is a known method of compensating for fluctuations in gas demand in natural gas networks consisting in compressing the intake gas to high pressure in periods of reduced gas demand, storing compressed gas and expanding the stored gas to the gas grid during periods of increased gas demand.

This method is characterized by high energy consumption for gas compression, as the compressors used to compress the gas are powered by electric or combustion engines, mainly gas engines. Therefore, it is mainly used in the nationwide networks to strategically compensate for fluctuating gas demand in seasonal cycles, associated with the summer - winter seasons.

According to the invention the technological layout of the installation for compensating fluctuations in gas demand in natural gas networks including compressor, storage of compressed gas and the pressure reduction module, is characterized by the fact that the used compressor is a reciprocating compressor driven by gas taken from a medium or high pressure transmission pipeline. Gas with reduced pressure from the compressor is directed to the low-pressure distribution pipeline, and compressed gas is stored in pressure tanks and during periods of increased gas demand the stored gas is being expanded and directed to the transmission pipeline.

According to the invention, the compression-storage-expansion installation is located at the network reduction station. The reciprocating compressor used in the method according to the invention is driven by the energy of the gas supplied from the medium or high pressure transmission pipeline, it can be single-sided or preferably double-sided, for example a compressor according to the patent description PL 235574.

Any pressure tanks can be used as storage tanks for compressed gas such as stationary tanks composed of bundles of steel or composite cylinders.

Preferably, the technological layout of the installation according to the invention includes additionally a measuring-distribution set, which is connected to the storage tanks to deliver compressed gas as CNG fuel to automotive vehicles.

Preferably, the technological layout of the installation according to the invention has additionally a gas liquefaction module based on gas expansion using the Joule-Thomson effect and at least one liquid gas vessel and evaporator.

Preferably, the technological layout of the installation according to the invention has additionally a measuring-distribution set, which is connected to the storage tanks, for the delivery of liquefied gas as LNG fuel to the external customers.

According to the invention, a method of compensating fluctuations in gas demand in natural gas networks is the compression of gas, which was taken from a medium or high pressure transmission pipeline during periods of the reduced gas demand, to high pressure whereby the energy used for the gas compression is the energy from medium or high pressure gas expansion. The compressed gas is being stored and during periods of increased gas demand the stored gas is being expanded and directed to the transmission pipeline, and the gas with reduced pressure from compression is being directed to the low-pressure distribution pipeline.

Advantageously, the stored compressed gas can be issued through a measuring-distribution set as an ecological CNG fuel (English for: Compressed Natural Gas) for motor vehicles.

According to the invention, in a method for compensating fluctuations in gas demand in natural gas networks, preferably additionally compressed gas is being liquefied through gas expansion using the Joule-Thomson effect, then the liquefied gas is being stored and during periods of increased gas demand it is being evaporated and introduced to the network.

Preferably, the stored liquefied gas can be issued through the measuring-distribution set as LNG fuel (English for: Liquefied Natural Gas) to the external recipients, for example as ecological fuel for automotive vehicles.

The use of the method according to the invention for compensating fluctuations in gas demand in natural gas networks and the technological layout of the installation based on this method enables energy-free compression and storage of the compressed gas, especially in dispersed end zones of the transmission pipelines, where the gas pressure drops caused by the increased gas demand most often occur, preventing the correct operation of the gas network.

Technological layout of the installation for compensating fluctuations in gas demand in natural gas networks and a method for implementing this compensation according to the invention will be explained in an example based on the drawing (Fig. 1) showing the block technological diagram of the installation with all the alternative options including network pressure reduction station.

Example. In commonly used solutions in gas networks the transmission pipeline 1 is connected by pipeline 2 with the entrance of the network reduction station 3, and the output of reduction station 3 is connected to the distribution pipeline 4. The input of a double-acting reciprocating compressor 5 is connected by pipeline 6 to the transmission pipeline 1, and the outlet from compressor 5 is connected by pipeline 7 with distribution pipeline 4. The outlet of compressed gas from compressor 5 is connected by a pipeline 8 with a storage tank 9. Outlet from the storage tank 9 is connected by a pipeline 10 through a pressure reduction module 11 with a transmission pipeline 1. A measuring-distribution set 12 is connected to the pipeline 10 for dispensing compressed gas as CNG fuel. Connected to the pipeline 10 via the pipeline 13 there is also a gas liquefaction module 14, which is based on gas expansion using the Joule-Thomson effect. Gas output with reduced pressure is connected by pipeline 15 with a distribution pipeline 4, and the liquefied gas outlet is connected by pipeline 16 with a set of low temperature storage tanks 17. Outlet from the storage tanks 17 is connected by pipeline 18 through evaporator 19 with the transmission pipeline 1. A measuring-distribution set 20 is connected to the pipeline 18 for delivering liquefied gas as LNG fuel.

The operation method of the technological installation for compensating fluctuations in gas demand in natural gas networks is as follows:
Natural gas is transported via a medium or high pressure transmission pipeline 1 at a pressure of typically 3 - 8 MPa. From this pipeline the gas is being taken to the network reduction station 3, where after reducing the pressure to usually below 0.35 MPa it is directed to the distribution pipeline 4. Also from the transmission pipeline 1, gas is being taken to a double-acting reciprocating compressor 5. A part of the gas taken from the transmission pipeline 1 is a working medium and as a result of the expansion it does the work of compressing the remaining part of the gas taken in. Usually the gas is compressed to a pressure above 20 MPa, most often up to 20 - 25 MPa. The expanded gas is directed to the distribution pipeline 4 and the compressed gas is directed to the storage tank 9 in the form of a parallel connected pressure cylinders. In the periods of increased gas demand compressed gas from the storage tank 9 is directed through the pressure reduction module 11 to the transmission pipeline 1.

The compressed gas from the storage tank 9 can be issued through the measuring-distribution set 12 as CNG fuel.

The compressed gas from the storage tank 9 can also be directed to a gas liquefaction module 14, which is based on gas expansion using the Joule-Thomson effect. Part of the gas is being liquefied in the gas liquefaction module 14 and the rest of the reduced pressure gas is directed to the distribution pipeline 4. The liquefied gas is directed to the low-temperature storage tanks 17. In periods of increased gas demand, liquefied gas from the tank storage 17 is directed through the evaporator 19 to the transmission pipeline 1.

Liquefied gas from the storage tanks 17 can be dispensed by measuring- distribution set 20 as LNG fuel.