GB2393669A

GB2393669A - A wet gas sampling apparatus

Info

Publication number: GB2393669A
Application number: GB0306332A
Authority: GB
Inventors: Mark Anthony Jiskoot
Original assignee: Jiskoot Autocontrol Ltd
Current assignee: Jiskoot Ltd
Priority date: 2002-10-04
Filing date: 2003-03-19
Publication date: 2004-04-07
Anticipated expiration: 2023-03-19
Also published as: GB0223037D0; GB0306332D0; GB2393669B

Abstract

A wet gas sampling apparatus comprises in a pipeline 100, a mixer 103, 104, for mixing the wet gas, a sampler 106, downstream of the mixer, a filter 31, to remove liquid from the sampled wet gas and apparatus 21 to measure the quantity of gas. In use, wet gas from a pipeline 100 is mixed and passes via a sampler which may be a hollow probe 107 preferably to one of two inlet ports 11, 12. Preferably following gas inlet port 11, the gas passes through selector valve 13, pass temperature gauge 15 through selector valves 16, through junction 19, past temperature gauge 24, through pressure control valves 25, 26 before exiting at an outlet 28. The wet gas may pass through the system until a steady state temperature is recorded at the temperature gauges 15 and 24. Advantageously the liquid content of a wet gas is determined by passing the gas through a valve 17 to a mole sieve 31 which removes liquid from the gas. Preferably dry gas is stored in a receiver 41 and is analysed for example by gas chromatography.

Description

1 2393669

WET GAS SAMPLING APPARATUS AND METHOD

BACKGROUND OF THE INVENTION

5 The present invention relates to a wet gas sampling method and apparatus.

The invention will be described with reference to sampling hydrocarbons from an oil gas pipeline but may be used in other environments in which a flow of wet gas is to be measured.

"Wet gas" in the petrochemical industry is the term normally used to describe gaseous hydrocarbons with a percentage of liquid which may be in the form of mist or free liquid. Thus, for example, wet gas may simply be a gas such as a hydrocarbon gas passing down a pipeline with a small amount of liquid in suspension in the form 15 of a mist or may also include a small amount of hydrocarbon liquid which would normally be present as free liquids in the bottom of the pipeline or other vessel in which the hydrocarbon gas is situated or as slugs of liquid or as an annular film around the circumference of the pipeline.

20 In a normal arrangement, the amount of liquid is less than 10% by volume of the wet gas and more typically in the range of 0-5%.

However, particularly in the case of hydrocarbons, the liquid content of the wet gas can be a very valuable. Indeed, even though it may only be 05% of the 25 volume, it can be the most valuable fraction of the hydrocarbon.

For reservoir management, allocation and taxation, it is necessary to determine both the quantity and the quality of the hydrocarbon. Currently the volume of dry gases are measured dynamically and the quality can be measured with an on line 30 analyscr with the liquid content ignored as both current online and offline measurement and analysis techniques do not work well with liquids. It is hard to

( 2 determine the liquid content or establish a predictable and measurable flow regime to the required accuracy.

It would therefore be desirable to provide a measurement apparatus in which 5 the wet gas is accurately sampled and both the gases and liquid fractions are retrieved in suitable quantities so as to provide accurate analysis of their relative quantity and composition. SUMMARY OF THE INVENTION

The present invention provides, according to the first aspect, a wet gas I sampling apparatus comprising a filter to remove liquid from a flow of wet gas and apparatus to measure the quantity of gas.

15 The filter may comprise a mole sieve, which may include liquid removing material such as zeolite, silica gel or activated charcoal. In the preferred arrangement the filter is removable from the wet gas sampling apparatus, whereby the filter may be weighed to determine the liquid held in the filter.

20 The apparatus to measure the quantity of gas may comprise a gas flow measuring apparatus to measure the mass of gas after it has passed through the filter.

There may be provided apparatus to collect the gas after passing through the filter. The collector apparatus may comprise a cylinder mounting a piston. the 25 cylinder having an entry end and a opposite end, gas to be collected passing into the entry end of the cylinder and forcing the piston to move from the entry end to the opposite end against a bias. The bias may be provided in the form of gas at lower pressure applied to the side of the piston opposite the entry end of the cylinder.

3() Where the wet gas is provided in the form of a flow of wet gas. for example a flow of wet gas in a pipeline, a mixing apparatus may be provided in the flowing wet

( 3 gas to mix the wet gas to provide a representative sample of the wet gas. The mixing means may comprise a venturi.

A sampler may be provided downstream of the mixing apparatus, said sampler 5 including entry means provided at plurality points across the wet gas flow whereby to sample the wet gas at the plurality of spaced points.

The present invention also provides, according to a further aspect, a method of sampling wet gas comprising filtering the wet gas to remove liquid from the flow of 10 wet gas and measuring the quantity of gas, and, preferably, the quantity of liquids and an analysis of the composition of independent liquid and gas samples I BRIEF DESCRIPTION OF THE DRAWINGS

15 The preferred embodiments of the invention are now described by way of example only and with reference to the accompanying drawings in which: Figure 1 is a front prospective view of part of a wet gas sampling apparatus in accordance with a preferred embodiment invention, with a front cover removed.

Figure 2 is a diagrammatic cross-section through a pipeline and sampler for use with the apparatus of Figure 1, and, Figure 3 is a diagrammatic cross section through molecular sieve heater for 25 recovering material trapped in a sieve.

DESCRIPTION OF PREFERRED EMBODIMENT OF THE INVENTION

Referring to Figure 1 there is shown a cabinet 10, which mounts many of the 30 components of the wet gas sampling apparatus.

Two inlets 11 and 12 are provided whereby gas from samplers in two different streams may be sampled. Inlet 11 is connected to a selector valve 13 and inlet 12 is connected to a selector valve 14. The outputs of the two selector valves 13 and 14 are connected by suitable piping to the inlets ofthree selector valves 16, 17 and 18. Fach 5 selector valve to be described in this embodiment is a double isolation valve which includes one or more handles which may be manually or mechanically (ie electrically or hydraulically closed) operated so as to open or close the relevant valve.

The piping between the selector valves 13 and 14 and selector valve 16, 17 and 18 10 includes a temperature gauge 15.

The output of selector valve 16 is connected by suitable piping to a junction 19 and thence to an input of a mass flowmeter 21 which measures the mass of gas passing therethrough. The output of the mass flovmeter 21 is connected to by 15 suitable piping into the inputs of selector valves 22 and 23, a temperature gauge 24 and the input of a pressure control valve 26 is connected via a selector valve 27 to an output 28 from the cabinet 10, the output 28 being connected to any suitable means such as a flare or back to a pipeline.

20 The downstream side of the selector valve 17 is connected by piping to the input of a first removable mole sieve 31. Each mole sieve may have integral isolation valves at its inlet and its outlet which would be open when the mole sieve is fitted to the sampling apparatus. The outlet of the mole sieve 31 is connected by suitable piping to selector valve 32 and thence to the junction 19 and to the mass flowmeter 25 21. Connected to the input piping of the mole sieve 31 is a pressure gauge 33 and similarly connected to the output piping of mole sieve 31 is a further pressure gauge 34. The downstream side of the selector valve 18 is similarly connected by suitable piping to a pressure gauge 36. a second removable mole sieve 37, a pressure 30 gauge 38. and a selector valve 39.

( 5 Each of the mole sieves 31 and 37 is coupled to its respective input and output pipings by means of a releasable coupling. Each mole sieve may comprise a packed tube of zeolites chosen in the required bead sizing and lattice size to optimise the flow of gas therethrough and the adsorption of liquid, and similarly the mole sieve length 5 and diameter and weight is optirnised to maximise the collection of the relevant liquid. The downstream side of the selector valve 23 is connected by a suitable flexible releasable coupling to the upstream side of a receiver 41, the opposite side of 10 the receiver 41 being connected by a releasable flexible coupling means to a selector valve 42. Respective pressure gauges 43 and 44 are mounted to measure the pressure in the couplings on each side of the receiver 41. Each receiver will be provided with integral valves to allow isolation and when mounted and coupled to the apparatus these valves will be open.

The receiver 41 comprises a cylinder 45 in which is mounted a freely moveable piston 46. Said opposite side of the selector valve 42 is connected by suitable piping to a pressure control valve 47 and thence to a selector valve 48, the opposite side of the selector valve 48 being mounted to a coupling 49 in the wall of 20 the cabinet IO, the coupling 49 being connected to a precharging supply of inert gas such as argon, indicated at 51.

There is provided a second receiver 61, the second receiver 61 being similar to and connected similarly between the downstream side of selector valve 22 and the 25 pressure control valve 47, there being provided similar parts as with the receiver 41, selector valve 62, pressure gauges 63, 64, cylinder 65, and t'reely movable piston 66.

Each of the inlets 11 and 12 is connected to a respective sampler mounted in a suitable wet gas supply, t'or example in a hydrocarbon gas pipeline from a gas rig.

A sampler will be described with reference to Figure 2.

( 6 A pipeline 100 for hydrocarbon gases is illustrated in axial crosssection, the hydrocarbon gas flowing from left to right as indicated by the arrow 101. The hydrocarbon is wet gas and the liquid fraction may be provided in the form of fine droplets and/or in a separated liquid fraction 102 at the bottom of the pipeline 100. In 5 order to provide representative sample there is provided in the pipeline 100 a mixing means which may be in the form of a venturi 103. Venturi 103 is in the form of a constricted throat. Other mixing means are envisaged, for example, a blade or sharp edge over which the gas and liquid flow or a mechanical turbo mixer in the form of, for example, a powered or unpowered rotatable propeller.

Downstream of the venturi 103, the wet gas and liquid fraction are mixed as is I indicated at 104. Further downstream of the venturi 103 there is provided a sampler 106 in the form of a hollow probe 107, the hollow probe 107 including a plurality of inlet ports 111-llS spaced at predetermined intervals across the diameter of the 15 pipeline 100. These inlet ports 111-115 are connected to suitable piping within the probe 107. The probe 107 is mounted in the side wall of the pipeline 100 by mounting means 1 16 and there is provided an outlet at 1 17. The outlet 1 17 may have separate pipes connected to each of the inlet ports 111-115 or a manifold may be provided in the head 118 so that the outlet 1 17 provides a proportion of the mixed wet 20 gas from each inlet port I I 1- 1 15. In any case, the outlet 1 17 is connected to one or other of the inlets 11 or 12 at which point inlet 11 or 12 receives a wet gas mixture which comprises a proportion of the wet gas from each of the inlet ports I 1 1-1 I S. It will be understood that with the arrangement to shown in Figure 2, by causing the mixing by virtue of the venturi 103 and sampling at different parts across the pipeline, 25 be a representative sample of gas/liquid is passed to the inlet I I and/or 12.

We will now describe operation of the apparatus of Figures I and 2.

In the apparatus of Figure 1. initially two sieves 31, 37 containing dry zeolite 30 or other material are weighed or then installed. Further two dry and clean receivers 41, 61 will be installed. Valves 48 and 42 will be opened allowing argon gas at a set

( 7 pressure lower than that at inlet 11 to displace piston 46 to the left, valve 42 is then closed. Wet gas from a relevant pipeline (ie pipeline 100) is passed via a suitable pipe 5 into the one or other of the inlets 11, 12. Assuming it is supplied to inlet 11, the selector valve 13 is opened thereby allowing the wet gas to pass through piping past the temperature gauge 15 to the upstream sides of the selector valves 16, 17 and 18.

Selector valve 16 is opened so that the wet gas passes to junction 19, then through the meter 21, past the temperature gauge 24 to the pressure control valves 25, 26 and I O thence to the selector valve 27 which when open allows the wet gas to pass out of the outlet 28. The pressure control valves 25, 26 can be used to establish the flow rate in the apparatus to optimise the collection rates in conjunction with the meter 21.

The wet gas is passed through this system until a steady state is recorded in 15 terms of the temperatures as recorded at the temperature gauges 15 and 24.

To measure the liquid content of a known quantity of wet gas, the selector valve 16 is closed and valves 17 and 32 are opened. At the same time a totaliser meter 20 in the mass flowmeter 21 is reset to zero.

Wet gas then passes via selector valves 13, 17 and 32, through the mole sieve 31, through the meter 21. The quantity (mass) of gas passing through the system is measured by the totaliser 20 of the meter 21. The sieve 31 removes the liquid from the wet gas whereby dry gas passes through to the remainder of the system.

The valves 23 and 42 are opened so there is an excess pressure to the left of the piston 46 in the cylinder 45 and the piston 46 moves from the left hand end of the cylinder 45 compressing the argon gas until the pressures are balanced, the speed of movement being controlled by the differential pressure between the opposite ends of 30 the receiver 41.

( 8 When sufficient gas has passed through the meter 21 valves 17 and 32 may be closed. Thus a predetermined mass of wet gas as measured by the meter 21 has passed 5 through the sieve 31. The receiver 46 and sieve 31 may be removed and the sieve 31 weighed thereby giving the mass of liquid which has been removed by the sieve from the relevant mass of gas as recorded by the meter 21.

The ratio of mass of liquid to gas in the wet gas may thereby be calculated.

10 The dry gases stored in the receiver 41 may be analysed in the normal way, for example by gas chromatography.

We have referred to the meter 21 as being a mass measuring meter. In practice, the meter 21 is normally a meter which measures the flow of gas through the 15 meter. This may be measured in a number of ways, including propeller driven by the flow of gas through the meter. The mass of the gas passing through the meter may be established by utilising the speed and flow of the gas, the known diameter of the meter, and the temperature and pressure of the gas as measured by the temperature gauges and pressure gauges. One may measure the liquid content of the wet gas from 20 either the inlet I I or 12 depending on whether the valve 13 or valve 14 is opened.

Subsequent similar measurements may be made to establish the composition within the sieve 37 and receiver 61.

25 In order to establish the composition within the mole sieves, the apparatus shown in Figure 3 may be used. Figure 3 is an axial crosssection through the heating apparatus 101. As is clear the heating apparatus 101 comprises, 2 x 1000kW ceramic fibre heaters of generally tubular form including a central bore 103. The ceramic heaters 102 are electric heaters and are controlled by control means 104. A manual 30 switch 105 is provided to isolate the heaters 102. The control means 104 cycles the

( 9 heaters to provide a controlled temperature rise and also includes an electronic temperature control indicator 106.

The ceramic heaters 102 are mounted within a insulating jacket 107 which has 5 an overall rectangular form.

A coiled pipe or gas coil 108 the outer diameter of which matches the inner diameter of the bore 103 is mounted within the bore 103. The inlet end of the gas coil 108 passing through the insulating jacket 107 to an inlet 109, the opposite end of the 10 gas coil 108 passing out of the bore 103 to a union 111. The opposite open ends of the bore 103 may be closed insulating plugs 1 12 and 1 13.

In use, one of the sieves 31, 37 the composition of whose liquid content is to be measured is removed from the apparatus of Figures 1 and 2, the relevant open ends 15 sealed, and then inserted into the apparatus of Figure 3. By way of illustration it will be seen that the sieve 31 is mounted in the heating apparatus 101 of Figure 3. The union 111 is then connected with one end opening (the inlet end) of the sieve 31 and an outlet pipe 114 is connected to the outlet at the opposite end of the sieve 31, the outlet pipe 114 being connected to a suitable analysing means such as a chromatic 20 analyser.

One way to remove and hence be able to analyse the liquid adsorbed in the mole sieve 31 is to heat the mole sieve 31 and vaporise the liquid. The difficulty is that unless the heating conditions are carefully controlled. the zeolite material within 25 the sieve will be damaged. It is necessary to heat the materials slowly to drive offthe adsorbed liquid and maintain the physical structure of the zeolite. If one simply heats the sieve 31 from the outside in the normal way, because of the insulating properties of the zeolite it is necessary to heat the zeolite slowly and it takes a considerable length of time to drive off all of the liquid within the sieve. The present arrangement 30 provides a two stage approach, that is heating the sieve from its outside surface by means of the electrical ceramic fibre heaters 102, and passing warmed dry inert gas

(argon) through the sieve to heat it from the inside. The coil 108 is used to heat the gas before it passes into the sieve.

Thus. in operation, after the sieve has been inserted into the heating apparatus 5 of 101 of Figure 3, the heaters 102 are set to increase temperature at a predetermined slow rate and inert gas such as dry argon or one that does not effect the analysis is passed from the inlet 109 through the coil 108 where it is heated, and then through the sieve 31 via the union I I l to the outlet pipe 1 14. In a typical arrangement the argon is set to flow at 2 litres per minute. However, nitrogen may be used.

The temperature of the sieve is measured so as to control the rate of increase of temperature by means of thermocouples 116 which are connected to control means 104 and indicator 106.

15 The invention is not restricted to the details of the foregoing example.

The system described has two copies of the collection vessels mole sieve and receiver) to allow a succession of samples to be taken to allow checks on the repeatability of the measurement. However, only a single sieve and only a single 20 receiver may be provided, and only a single inlet may be provided.

It is also possible that a continuous loop from the process may be established so that the system may be configured to take many small volumes of sample over a protracted period that may better represent temporal fluctuations in the quality of the wet gas Whilst we have described an arrangement in which the all of the selector valves are manually operated, they may be operated by electrically drived motors or by pneumatic or hydraulic motors.

Claims

( CLAIMS:

1. A wet gas sampling apparatus to sample wet gas from a flow of wet gas in a pipeline, said apparatus comprising: 5 in a pipeline, a mixer for mixing the wet gas to provide a representative sample of the wet gas; a sampler provided in the pipeline downstream of the mixer; means to pass the wet gas from the sampler to a filter to remove liquid from the flow of wet gas, and; 10 apparatus to measure the quantity of gas.

2. A wet gas sampling apparatus as claimed in claim 1 in which the filter comprises a mole sieve.

15

3. A wet gas sampling apparatus as claimed in 2 in which the mole sieve comprises liquid removing material selected from zeolite, silica gel or activated charcoal.

4. A wet gas sampling apparatus as claimed in any of the claims I to 3 in which 20 the filter is removable from the wet gas sampling apparatus, whereby the filter may be weighed to determine the weight of liquid held in the filter.

5. Apparatus as claimed in any of the claims I to 4 in which the apparatus to measure the quantity of gas comprises a gas flow measuring apparatus to measure the 25 mass of gas after it has passed through the filter.

6. Apparatus as claimed in any of the claims 1 to 5 further comprising an apparatus to collect the gas after passing through the filter, the collector apparatus comprising a cylinder mounting a piston, the cylinder having an entry end and an 30 opposite end, gas to be collected passing into the entry end of the cylinder and forcing the piston to move from the entry end to the opposite end against a bias.

(

7. Apparatus as claimed in claim 6 in which the bias is provided in the form of gas at lower pressure applied to the side of the piston opposite the entry end of the cylinder. 5

8. Apparatus as claimed in any of the claims I to 7 in which said sampler includes entry means provided at a plurality of points across the wet gas flow whereby to sample the wet gas at a plurality of spaced points across the pipeline.

9. A method of sampling wet gas comprising: 10 in a pipeline' mixing the wet gas to provide a representative sample of the wet gas; sampling the wet gas in the pipeline downstream of the mixer; filtering the sampled wet gas to remove liquid from the flow of wet gas and; measuring the quantity of gas and the quantity of liquid.