DE102012008423A1 - Device for sampling aggregate gas distribution network under increased pressure in gas grid, has flow resistor provided in flow path of gas and passed through gas with sound velocity so as to adjust mass flux during sampling operation - Google Patents

Abstract

The device (3) has an isolatable sample container (12) embedded into a flow path of gas during sampling operation. A flow resistor (10a) is provided in the flow path of the gas during the sampling operation and passed through the gas with sound velocity to adjust constantly mass flux during the sampling operation. The flow resistor is designed as a critically propelled nozzle and critically propelled pinhole. A pneumatic propelled control valve (9a) for a cyclic sampling is provided in the flow path of the gas during the sampling operation. Independent claims are also included for the following: (1) a method for aggregated sampling of gas under increased pressure in a gas grid (2) a method for determining middle gas composition.

Description

The invention relates to a device for aggregated sampling of gas, which is located under elevated pressure in a gas line network, with a lockable sample container which can be incorporated during sampling in the flow path of the gas. Furthermore, the invention relates to a method for aggregated sampling and a method for determining the average gas quality after completion of the method for aggregated sampling.

The composition of natural gas in a gas pipeline network, in particular in a gas transport network or gas transmission network (pressure level about 50 to 60 bar), can vary significantly depending on the origin of the natural gas and also be subject to temporal variations.

Furthermore, increasing trade in conjunction with a growing import of liquefied natural gas (LNG), which is transported by ship to Europe, has for some years seen increasing fluctuations in the gas quality and thus also in the calorific value of the transported natural gases ( K. Altfeld and P. Schley: Development of Natural Gas Properties in Europe. gwf Gas / Natural Gas, 152 (2011), pp. 544-550 ). As a result, there are increasingly situations in which gas in gas distribution networks (pressure level about 10 to 25 bar) from two or more gas transport lines with different calorific values is fed (so-called multi-page feed). In addition, biogas is increasingly generated, which is usually fed directly into the gas distribution networks. Against this background, it is becoming increasingly difficult to determine in gas distribution networks the calorific value of the supplied gas required for the billing of an end customer.

The billing of end customers in supply areas is carried out in Germany in accordance with the DVGW Code of Practice G685 DVGW, Gas Billing, DVGW Technical Rules, September 2008. The calorific values of the transported natural gas are usually measured at representative locations in the gas transport network. As a rule, process gas chromatographs are used here, which analyze the gas discontinuously (eg every 5 min) in relation to the composition and the calorific value from the proportions of the gas components ISO 6976 to calculate.

For some years, so-called condensing boiler systems for gas transport networks have also become established ( K. Altfeld, J. Bödeker, H. Frieling, P. Schley and M. Uhrig: Modeling Gas Flow in Pipelines Tracking Gas Quality. Proceedings of the 2008 International Gas Research Conference, Paris (2008) ). These systems allow a calculatory determination of the calorific value at any time and at any location in the entire network. This requires measurements of the calorific value at the feed-in points as well as the volumes at the entry and exit points. The calorific value reconstruction systems are validated by means of defined reference measuring points, at which the calorific value is measured and compared with the calculated value. Methods for calculating the calorific value in distribution grids are currently still in development ( P. Schley, J. Schenk and A. Hielscher: Calorific value tracking in distribution grids: Part 1: Development and validation of the method. gwf The gas and water sector Gas-natural gas Jg. 152, 2011 p. 552-556 and J. Schenk, P. Schley, A. Hielscher, C. Fernandez and S. Mäurer: Brennwertverfolgung in Verteilnetzen. Part 2: Evaluation field trial and implementation. gwf The gas and water compartment, natural gas, Jg .: 152, 2011 p. 676-683 ,

From practice, devices for aggregated sampling, so-called sample collectors are known. These are used for sampling to directly determine the calorific value of a service area for the purpose of billing customer gas consumption or to validate values from condensing boiler reconstruction systems.

In the known sample collectors, a defined amount of gas is cyclically introduced into a sample vessel or a sample container during sampling by means of an electrically operated piston-cylinder system. At the beginning of sampling, the sample vessel is evacuated. Upon completion of sampling, the sample vessel is removed and a portion of the gas sample is applied to a gas chromatograph. From the gas composition determined in this way, it is then possible to calculate the calorific value representative of the period of the sampling or other gas quality characteristic values. The advantage of such sampler is the comparatively low cost.

In gas distribution networks, sample collectors that require an external power supply can hardly be used, since many gas pressure regulating stations, on which a sampling is basically possible, have no electrical power supply. Also problematic is the necessary prior Evacuation of the sample container. The negative pressure can easily lead to contamination and thus to a distortion of the sample, for. B. in that air is introduced into the sample container due to leaks. This leads to difficulties and inaccuracies in the subsequent gas chromatographic analysis of the sample.

The object of the invention is therefore to provide a simple and practical device of the type mentioned above, which works without external power supply and to provide a method for aggregated sampling and for determining the average gas quality after completion of the method for aggregated sampling at the disadvantages of the prior art are avoided.

The object is achieved by the device according to the features of the claims 1 and 5 and procedurally by the features of the claims 10 and 11.

In the flow path of the gas, a constant mass flow is set by means of a flow resistance during the sampling, which is independent of the pressure behind the flow resistance or the pressure in the sample container. In this way, no power is required for sampling.

According to claim 1 is in the flow path of the gas during sampling a flow resistance, which can be traversed by the gas at the speed of sound, to set a constant mass flow during sampling. During sampling, the gas flows through the flow resistance at the speed of sound, so that the mass flow is constant irrespective of the pressure behind the flow resistance.

Preferably, the flow resistance is designed as a critically operated nozzle, which is also referred to as a critical nozzle or Laval nozzle. In such nozzles, the passage cross-section decreases steadily from entry to a narrowest cross-section. The gas flows in the narrowest cross-section of the nozzle exactly with the speed of sound, as long as the ratio between the pressure behind the critical nozzle to the pressure in front of the critical nozzle does not fall below the critical pressure ratio of about 0.5. The mass flow is constant regardless of the pressure in the sample container.

The complete thermodynamic description of a critical nozzle flow is the publication of P. Schley: Thermodynamic material quantities of natural gases to describe a critical nozzle flow. VDI Progress Reports, Series 7, No. 418 (2001) VDI Verlag Dusseldorf , refer to.

For simplification, a critically operated pinhole can be used instead of a critical nozzle. It should only be considered that the critical pressure ratio assumes slightly lower values.

An advantageous development of the invention is that in the flow path of the gas during sampling a pneumatically operated control valve for the purpose of cyclic sampling is. For example, the control valve can be set to sample 4 times per hour for 1 minute.

According to claim 5 is alternatively in the flow path of the gas during sampling a flow resistance, which is designed as a capillary, wherein by means of a pressure regulator, the pressure is controlled before flow resistance as a function of the pressure behind the flow resistance to set a constant mass flow during sampling.

According to the invention, the flow resistance and the sample container can form a structural unit. In this way, a very compact device can be realized.

Preferably, the removal opening of the gas line network is designed as a branch line. The sample container can be connected to the branch line. Thus, the sampling takes place in a partial flow of the gas and not in the main flow in the gas pipeline network.

In a preferred development, a pressure regulator is arranged in the flow path of the gas during sampling, which keeps constant a pressure adjustable before the flow resistance. The pressure is preferably reduced to a pressure lower than that prevailing in the gas mains.

The method for aggregated sampling with the device according to the invention is characterized in that the sample container is filled at the beginning of the sampling with helium at ambient pressure.

• a) ein Teil der Gasprobe auf einen Gaschromatografen aufgegeben wird, der Helium als Trägergas verwendet,
• b) zunächst die unnormierten Gasbestandteile (außer Helium) ermittelt werden,
• c) die Gasbestandteile normiert werden, indem jede Gaskomponente durch die Summe der unnormierten Gasbestandteile geteilt wird,
• d) der Brennwert sowie weitere Gasbeschaffenheitskennwerte aus der Gaszusammensetzung berechnet werden.

In the context of the invention, a method is provided for determining the average gas quality after the aggregate sampling process has been completed, which is characterized in that, after completion of the sampling, the mean gas composition of the gas sample in the sample container is determined by means of a gas chromatographic analysis

• a) a part of the gas sample is fed to a gas chromatograph using helium as a carrier gas,
• b) first the unnormalized gas components (except helium) are determined,
• c) the gas components are normalized by dividing each gas component by the sum of the abnormal gas components,
• d) the calorific value and other gas quality parameters are calculated from the gas composition.

The invention will be explained in more detail below with reference to preferred embodiments of the device according to the invention in conjunction with the drawing.

The drawing shows in:

1 a schematic representation of a first embodiment of an apparatus for aggregated sampling from a natural gas distribution network;

2 a schematic representation of a second embodiment of an apparatus for aggregated sampling from a natural gas distribution network.

In 1 is a gas pipe 1 with a pressure reducing station 2 shown. The gas line 1 is part of a public natural gas distribution network, in which the natural gas is under elevated pressure in a range of about 10 to 26 bar upstream of the pressure reducing station 2 stands. A schematically illustrated device 3 for aggregated sampling is in a trained as a branch line removal opening 4 involved. The branch line 4 is to the gas line 1 upstream of the pressure reducing station 2 connected.

In the embodiment according to 1 are in the branch line 4 one after the other a pressure regulator 5 , a filter 6 , a check valve 7 and one (optional) bypass line 8th , a control valve 9a and a flow resistance in the form of a critical nozzle 10a , a first shut-off valve 11 , a sample container 12 and a second shut-off valve 13 arranged.

About a pressure regulator 5 will be in the gas line 1 prevailing pressure in the branch line 4 to a pressure of z. B. 8 bar reduced. At this pressure, the gas is through a flow resistance 10a directed. The flow resistance can be traversed by the gas at the speed of sound to achieve a constant mass flow during sampling, regardless of the pressure in the sampling container.

At the in 1 illustrated embodiment is the flow resistance 10a as a Laval nozzle, hereinafter referred to as critical nozzle, with a diameter of z. B. 30-100 microns formed. As long as the ratio between the pressure downstream of the critical nozzle and the pressure upstream of the critical nozzle does not fall below the critical pressure ratio (depending, inter alia, on the type of nozzle), the gas flows at the speed of sound in the narrowest section of the nozzle. In this way, a constant sampling flow - more precisely mass flow - can be achieved, which in particular is independent of the pressure in the sample container. The critical pressure ratio of a critical nozzle is about 0.5. Thus, in the present example, the sample container can be filled to a pressure of 4 bar without the sampling flow being affected by the increasing sample pressure in the sample container.

So that a sufficiently large sampling period can be realized until the critical pressure ratio is reached, is via a pneumatically operated control valve 9a a cyclic sampling flow is set. For example, the control valve 9a adjusted so that the sampling takes place 4 times per hour for 1 minute. To the critical nozzle 10a To protect against soiling is in front of the critical nozzle 10a the filter 6 built-in.

The components of the embodiment according to 2 are, as far as the components in 1 match, indicated by the same reference numerals.

At the in 2 illustrated embodiment is the flow resistance 10b instead of a critical nozzle designed as a capillary. This allows the setting of very small flow rates, which is why even with a longer sampling period, a continuous flow can be realized and thus the control valve 9a of the embodiment in 1 can be omitted. The mass flow can be calculated approximately using Equation 1 using the law of Hagen-Poiseuille. Since the mass flow through the capillary depends both on the difference between the initial and the back pressure and on the density of the gas, the pre-pressure of the capillary is controlled by a pneumatic pressure regulator 9b regulated as a function of the back pressure of the capillary.

The characteristic of the pressure regulator is determined according to a constant mass flow.

Where ρ is the density, V is the volume flow and p is the pressure.

According to the invention, the sample container is filled with helium at ambient pressure at the beginning of the sampling. This avoids possible contamination of the gas sample by an entry of air due to leaks. In the subsequent gas chromatographic analysis of the sample, the influence of the previously filled helium can be easily eliminated. As a rule, gas chromatographs are used which use helium as the carrier gas. The presence of helium thus only leads to slightly smaller peak areas in the chromatograms of the analyzed gas components. By normalizing the mole fraction to 100%, however, this effect can be fully compensated.

Variations are possible within the scope of the invention. Thus, for convenience, instead of a critical nozzle, a pinhole can also be used. It should only be considered that the critical pressure ratio assumes slightly lower values.

LIST OF REFERENCE NUMBERS

1

gas pipe

2

pressure reducing station

3

Device for sampling

4

branch line

5

pressure regulator

6

filter

7

check valve

8th

Bypass line (optional)

9a

pneumatically driven control valve

9b

pneumatically driven pressure regulator

10a

critical nozzle

10b

capillary

11

first shut-off valve

12

sample container

13

second shut-off valve

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited non-patent literature

• K. Altfeld and P. Schley: Development of Natural Gas Properties in Europe. gwf gas / natural gas, 152 (2011), pp. 544-550 [0003]
• ISO 6976 [0004]
• K. Altfeld, J. Bödeker, H. Frieling, P. Schley and M. Uhrig: Modeling Gas Flow in Pipelines Tracking Gas Quality. Proceedings of the 2008 International Gas Research Conference, Paris (2008) [0005]
• P. Schley, J. Schenk and A. Hielscher: Calorific value tracking in distribution grids: Part 1: Development and validation of the method. gwf The natural gas and water gas and natural gas Journal 152, 2011 pp. 552-556 [0005]
• J. Schenk, P. Schley, A. Hielscher, C. Fernandez and S. Mäurer: Brennwertverfolgung in Verteilnetzen. Part 2: Evaluation field trial and implementation. gwf The gas and water compartment, Gas Natural Gas, Jg. 152, 2011 pp. 676-683 [0005]
• P. Schley: Thermodynamic material quantities of natural gases to describe a critical nozzle flow. VDI Progress Reports, Series 7, No. 418 (2001) VDI Verlag Düsseldorf [0014]

Claims (11)

Apparatus for the aggregated sampling of gas which is exposed to elevated pressure in a gas pipeline network ( 1 ), with a lockable sample container ( 12 ), which can be incorporated into the flow path of the gas during sampling, characterized in that a flow resistance (in the flow path of the gas during sampling) ( 10a ), which is traversed by the gas at the speed of sound, in order to set a constant mass flow during sampling. Device according to claim 1, characterized in that the flow resistance ( 10a ) is designed as a critically operated nozzle. Device according to claim 1, characterized in that the flow resistance ( 10a ) is designed as a critically operated pinhole. Device according to one of claims 1 to 3, characterized in that in the flow path of the gas during sampling a pneumatically operated control valve ( 9a ) for cyclic sampling. Apparatus for the aggregated sampling of gas which is exposed to elevated pressure in a gas pipeline network ( 1 ), with a lockable sample container ( 12 ), which can be incorporated into the flow path of the gas during sampling, characterized in that a flow resistance (in the flow path of the gas during sampling) ( 10b ), which is designed as a capillary and that by means of a pressure regulator ( 9b ) the pressure before the flow resistance as a function of the pressure behind the flow resistance ( 10b ) in order to set a constant mass flow during sampling. Device according to one of claims 1 to 5, characterized in that; that the flow path of the gas as a branch line ( 4 ), which are connected to the gas pipeline network ( 1 ) connected. Device according to one of claims 1 to 6, characterized in that in the flow path of the gas during sampling a pressure regulator ( 5 ), which has an adjustable pressure upstream of the flow resistance ( 10a . 10b ) keeps constant. Device according to one of claims 1 to 7, characterized in that in the flow path of the gas in the sampling before the flow resistance, a filter ( 6 ) is arranged. Device according to one of claims 1 to 8, characterized in that the flow resistance ( 10a . 10b ) and the sample container ( 12 ) form a structural unit. Method for aggregated sampling with a device according to one of claims 1 to 9, characterized in that the sample container ( 12 ) is filled with helium at ambient pressure at the beginning of the sampling. Method for determining the mean gas quality after completion of the method for aggregated sampling according to claim 10, characterized in that after completion of the sampling, the mean gas quality of the gas sample in the sample container ( 12 a) a portion of the gas sample is applied to a gas chromatograph using helium as the carrier gas, b) first the unnormalized gas constituents except helium are determined, c) the gas constituents are normalized by adding each gas component is divided by the sum of the abnormal gas components, d) the calorific value and other gas quality parameters are calculated from the gas composition.

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