WO1995033020A1

WO1995033020A1 - Adding odorants to consumer gases in supply lines

Info

Publication number: WO1995033020A1
Application number: PCT/SE1995/000600
Authority: WO
Inventors: Erik SMÅRS
Original assignee: Erik Smårs Konsult Aktiebolag
Priority date: 1994-05-27
Filing date: 1995-05-26
Publication date: 1995-12-07
Also published as: SE9401827D0; SE9401827L; SE501823C2; AU2634495A

Abstract

The invention relates to method and means for adding an odorant to a consumer gas flowing in pipelines, in order to warn people in the surroundings of consumer sites or gas supply lines of the risk of fire, explosion or other danger, if consumer gas is escaping into the surroundings due to leakage or incautiousness. The odorant is added to the consumer gas in the pipeline (1) in liquid form in proportion to the consumer gas flow rate by means of a pump (18) and an instrument for odorant flow rate control (7). The process control is taken care of by a computerized central process unit (8). The invention is characterized by the following features. Inert gas is first supplied to a pressure vessel (3 or 4) to a pressure slightly higher than the pressure in the consumer gas pipeline. Odorant liquid is then transferred from a storage vessel (19) to the pressure vessel (3 or 4) by means of the pump (18) in such an amount that the pressure becomes considerably (2-20 times) higher than the pressure in the pipeline. By means of this overpressure odorant is supplied from the pressure vessel to the consumer gas pipeline (1). The amount of inert gas that is dissolved into the odorant by the high pressure in the pressure vessel and gets lost is restored in correct amount from a high pressure inert gas cylinder (16).

Description

Adding Odorants to Consumer Gases in Supply Lines

Field of Invention

The present invention relates to a method of adding an odorant to a consumer gas flowing in a gas pipe line. The intention with the added odorant is to warn people in the vicinity of a site for gas consumption or of pipelines transferring gas for the risk of fire, explosion, poisoning, asphyxiation or some other danger, if consumer gas is escaping into the surroundings due to leakage or incautiousness. The odorant, preferably an organic sulphur compound in liquid form, is taken from a storage vessel and is pumped into a pressure vessel partly filled with inert gas. The overpressure in the pressure vessel is then forcing odorant through an instrument for controlling the flow rate into the gas pipeline. The odorant evaporates in the gas pipeline. By means of a gas-flow-rate meter in the pipeline and the flow rate controlling instrument mentioned above odorant is injected into the pipeline in proportion to the gas flow rate. The invention also relates to an arragement for earring out the method.

Background of the Invention The concept of adding odorants to consumer gases in accordance with the aforegoing, so as to indicate the leakage of explosive or poisonous gases for instance has long been known to the art. Examples of gases which are odorized in this way are natural gas and town gas, which if leaking to the surroundings can cause extremely severe accidents by fire or explosion. The method of adding an odorant into the flowing gas in a pipeline, that is most used today, is to use a dosage pump that pumps the odorant in liquid form from a storage vessel to an injection nozzle in the pipeline, where it vaporizes more or less rapidly. In order to get required constant concentration of odorant in the gas, the dosage pump is controlled by a signal from a gas-flow- rate meter in the gas pipeline in such a way that the flow of odorant into the pipeline is proportional to the gas flow rate.The concentration of odorant in the gas is ususally adjusted by manual adjustment of the piston stroke of the dosage pump. However, this method and other known solutions with manually adjusted dosage pump do not satisfy the demands of today for among other things remote control of the odorization process. In addition, a piston or membrane pump does not give a continuous injection of odorant into the gas but an intermittent flow. An additional drawback with these solutions is that the odorization process is interupted when the dosage pump has to be disconnected for service or exchange. Objects of the Invention

The main objects of the present invention is to propose a method that gives possibilities for remote control of the odorization process, that gives continuous flow of odorant into the gas, and that makes uninterupted injection of odorant possible during a considerable time even while the odorant pump is disconnected for service or exchange. Another object is to provide an arrangement which can be used when applying the method according to the invention.

Disclosure of the Invention

The aforesaid objects are achieved in accordance with the present invention by using a process in combination with a computerized central process unit (CPU) described as follows. By a pump of simple design the odorant liquid is pumped from the odorant storage vessel into a pressure vessel, which has its inlet and outlet at the bottom, and which, before filling with odorant, has been pressurized with inert gas to a pressure somewhat higher than the pressure in the gas pipeline. The pressure vessel is filled with such an amount of odorant liquid that the pressure is considerably (2 - 20 times) higher than the pressure in the gas pipeline. This overpressure is then used to force odorant liquid from the pressure vessel through an instrument for control of the flow rate into the gas pipeline. Thus, according to the invention, the odorant additive is not controlled by a dosage pump but by a control valve integrated into the instrument giving a continuous odorant flow rate. The pump can be made to always operate with one and the same flow rate, choosen such that the filling of the pressure vessel is performed in a time that is short in comparison with the time it takes to consume the content of a "full" pressure vessel when the gas flow rate is at its maximum.

By using two pressure vessels alternately one of them can deliver odorant to the pipeline while the other one can be refilled. In this way there is no interuption in the supply of odorant to the pipeline, and there is almost always a filled pressure vessel, that can deliver odorant to the pipeline if service or exchange of pump is needed.

Due to the high pressure in the pressure vessels some of the inert gas will dissolve into the odorant liquid and get lost to the pipeline. This loss has to be compensated for. This is done by filling the pressure vessel with the correct amount of inert gas from a high pressure cylinder before filling the pressure vessel with odorant. Other characteristics of the method according to the invention and of the arrangement for applying the method is clarified from the patent claims that are found in a later section.

The invention will now be described in more detail with reference to an exemplifying embodiment of the invention and also with reference to the accompanying drawing.

Description of a Preferred Embodiment of the Invention 1 in the enclosed figure represents a supply line with flowing consumer gas, for instance natural gas, which is to be odorized. This is done through a conduit 2, which transfers odorant from a pressure vessel 3 or 4 via a stop valve 5 or 6 and a flow controlling instrument 7, containing among other things one or more flow rate meters, one or more control valves and a pressure regulator that keeps the pressure fall across the control valve(s) on a constant level. The odorant can consist of an organic sulphur compound in liquid form. It is taken out from the pressure vessel 3 or 4 through an opening in its bottom. It is forced into the supply line 1 by means of the overpressure that is created when the pressure vessel is filled, first with inert gas from a high pressure inert gas cylinder 16 to a pressure slightly higher than the pressure in the gas supply line, then with odorant liquid from a storage vessel 19 to a pressure that is considerably (2 - 20 times) higher than the pressure in the gas supply line. The flow-controlling instrument 7 is governed by a computerized central process unit 8 in dependance of the flow rate of consumer gas in the supply line 1 as measured by the flow rate meter 9.

Only one of the valves 5 or 6 is open at a time. When such an amount of odorant in one of the pressure vessels, for instance 4 with valve 6 open, has been used up, so that its excess pressure over the gas supply line has become small, valve 6 is closed and valve 5 opens to pressure vessel 3, which already is filled and which continues immediately to supply odorant to the gas supply line 1. The valves 5 and 6 are governed by the central process unit 8 in dependance of the pressure in the pressure vessels 3 and 4 by means of pressure transmitters 10 and 11 and in dependance of the pressure in the gas supply line 1 by means of pressure transmitter 12.

As soon as one of the pressure vessels 3 or 4 is "empty" so that corresponding valve 5 or 6 is closed as described in the previous paragraph, the other valve 13 or 14 connected to the "empty" pressure vessel is opened as well as a flow limiting valve 15 connected to a high pressure cylinder 16 with inert gas. Inert gas is supplied to the "empty" pressure vessel 3 or 4 in an amount that corresponds to the amount of inert gas that has been dissolved into the odorant liquid and got lost to the gas supply line since previous time inert gas was supplied to the pressure vessel. According to a separate description in the next section the pressure vessel is filled with inert gas to a pressure Pj as given by the following expression: P, = P. * (1 - P„ P„) * V/M₀ (0) where P₀ is the pressure in the gas supply line 1 plus the constant pressure fall across the control valve(s) integrated in the flow controlling instrument 7 as governed by the pressure regulator also integrated in the instrument 7. P_m is a constant maximum pressure to which the pressure vessel is to be pumped with odorant liquid.

V is the total inner volume of the pressure vessel and M_o is the volume (amount) of odorant that has passed out of the pressure vessel during the latest moment of emptying and that has been recorded by the central process unit by integration of the signal from a flow rate meter integrated in the flow controlling instrument 7. When the pressure Pi is reached the valve 15 is closed by a signal from the central process unit.

The valve 17 is then opened and pump 18 starts to pump odorant liquid from the odorant storage container 19 to the pressure vessel that just has been filled with inert gas. The pumping goes on until the pressure in the pressure vessel has reached the value P_m which must not exceed the maximum operating presure for the pressure vessel.

The process described above with refilling of the pressure vessels is repeated each time one of them has been "empty" so that the pressure has fallen to the value P₀.

In the case that the solubility of the inert gas in the odorant liquid is low the process with refilling of the pressure vessels is programmed in such a way that refilling with inert gas is performed only after they have been filled with only odorant liquid a number of times.

In addition to the functions and components described above the method and arrangements according to the invention includes necesarry stop valves for service and exchange of components, necesarry safety valves and other devices that facilitates the performance of the odorization process. The pressure for filling the pressure vessels with inert gas

The expression (0) above for the pressure to which the pressure vessels are to be filled with inert gas is derived as follows:

The pressure vessel with the inner volume V is here first assumed to be filled with inert gas to the pressure P₀ (see above) and thereafter with the volume v of odorant liquid, whereby the pressure becomes P. With the condition that the inert gas is following the ideal gas law, that the temperature is constant and that the vapour pressure of the liquid is negligible, the following relation would be valid, if no inert gas were dissolved in the liquid:

P„ * V = P * (V - v) (1)

Since part of the inert gas is dissolved into the liquid, the volume of the gas phase (V - v) at the pressure P will become less than is given by equation (1). We can make equation (1 ) valid by writing P₀ * V = P * k * (V - v) (2) where k (< 1 ) is a parameter that describes the solubility of the inert gas in the liquid. We can rewrite equation (2) in this way v/V = 1 - P„/(k * P) (3)

Then also the following equation is valid

where v_m is the volume of liquid at the maximum pressure P_m. Subtraction (4) - (3) gives v_m - v = P_o * V * (l/P - l/P_ιn)/k (5)

M = v_m - v in equation (5) is the volume of liquid that has left the pressure vessel while the pressure has decreased from P_m to P. This volume can be measured by integration of the signal from the flow rate meter for odorant liquid. The pressure P is measured by pressure transmitter.

M„ = v_m - v₀ = P„ * V * ( 1/Po - 1 /P_m)/k (6) is the volume of the liquid that has left the pressure vessel during the time when the pressure has decreased from P_m to P₀. Since M_β, P₀, P_m and V are known and measurable quantities, k can be calculated from this formula

When filling with inert gas after the pressure vessel has been emptied of odorant, compensation for gas lost through solution in the liquid can be made by filling to a pressure Pi that is k times larger than P₀, i.e.

Pi = k * P„ = Po * ( 1 - Po/P * VI M„ (0)

Recording of measured quantities and performance of the necesarry calculations are performed during the process by the computerized central process unit.

Claims

1. A method of adding an odorant to a consumer gas flowing in a gas supply line with the intention of warning people in the surroundings of a consumer site or a supply line for the risk of fire, explosion, poisoning, asphyxiation or other danger in case that gas is escaping into the surroundings due to leakage or incautiousness, wherein the odorant in concentrated liquid form, preferably an organic sulphur compound, is transferred to the consumer gas supply line from an odorant container with or without overpressure by means of a pump, flow rate meter, control valve and pressure regulator in proportion to the flow rate of the consumer gas in the supply line, and wherein the process control is automatically performed by a computerized control unit, characterized by the features

(a) that the odorant in liquid form, by means of the pump mentioned above is transferred to a pressure vessel that in advance has been pressurized with inert gas to a pressure somewhat higher than the pressure in the gas supply line and that it has its input and output opening in the bottom,

(b) that odorant is transferred to the pressure vessel mentioned in such an amount that the pressure is considerably higher than the pressure in the supply line,

(c) that the odorant then is transferred to the gas supply line through the flow rate meter, control valve and pressure regulator by the overpressure in the pressure vessel, and

(d) that the fraction of the inert gas in the pressure vessel, that at the high pressure is dissolved into the odorant and lost to the supply line, before refilling of odorant in the pressure vessel, is compensated for by filling inert gas from a high pressure gas cylinder with inert gas.

2. A method according to claim 1, characterized by the feature that the pressure vessel is refilled with inert gas to a pressure that is determined by the amount of inert gas that has been dissolved into the odorant and lost to the gas supply line.

3. A method according to claims 1 and 2, characterized by the feature that the pressure vessel is refilled with inert gas to a pressure P, given by the formula

Pι = Po * (l - Po P_m) * V/ M₀ where P₀ is the pressure in the gas supply line plus the pressure fall across the control valve as controlled by the pressure regulator, P_m is the maximum pressure to which the pressure vessel is pumped with odorant liquid,

V is the total inner volume of the pressure vessel, and M₀ is the volume (amount) of odorant, that during the last emptying of the pressure vessel has passed out from it and that is measured by integration of the signal from the odorant flow rate meter.

4. A method according to claims 1, 2, and 3, characterized by the feature that at least two pressure vessels for odorant, pressurized with inert gas, are used, and that uninterupted supply of odorant to the gas supply line is secured by means of valves that are operated in such a way that the pressure vessels are connected alternately for filling with odorant and inert gas and alternately for supply of odorant to the gas supply line.

5. A method according to claims 1, 2, 3, and 4, characterized by the feature that the pressure vessel(s) are filled with odorant to a pressure equal to or close to the maximum operating pressure of the vessel.

6. A method according to claims 1, 2, 3, 4, and 5, characterized by the feature that pressure vessels are used which are approved for an operating pressure of at least 200 bar.

7. An arrangement for adding an odorant to a consumer gas flowing in a gas supply line with the intention of warning people in the surroundings of a consumer site or a supply line for the risk of fire, explosion, poisoning, asphyxiation or other danger in case that gas is escaping into the surroundings due to leakage or incautiousness, which arragement, to attain required concentration of odorant in the consumer gas, comprises pump equipment to create the pressure that is required for supplying odorant into the gas supply line, equipment for measuring the liquid odorant flow rate, equipment for control of the liquid odorant flow rate, equipment for pressure controls, equipment for pressure measurements as well as equipment for automatic calculations and for automatic computerized control of the process, characterized by the features

(a) that it comprises a high-pressure vessel, to which liquid odorant is pumped with high pressure, which pressure is beeing used to force odorant into the gas pipeline through flow meter(s), control valve(s) and a pressure regulator,

(b) that it comprises arrangement for supplying inert gas from a high pressure inert gas cylinder into the high pressure vessel before the latter is filled or refilled with liquid odorant, (c) that it comprises a computerized central process unit, that is programmed for controlling the pressure when filling inert gas into the pressure vessel as well as the pressure when filling liquid odorant into the pressure vessel,

(d) that the computerized central process unit is programmed in such a way that it records the amount of odorant that is taken out from the pressure vessel during the empying sequence before filling with inert gas and that it calculates and controls the pressure to which the pressure vessel is to be filled with inert gas for compensating the loss of inert gas that occurs due to dissolution of gas into the liquid odorant.

8. An arragement according to claim 7, characterized by the feature that the computerized central process unit is programmed in such a way that, when filling the pressure vessel with inert gas, this is done to a pressure Pi that is given by the formula P_ι = P„ * (l - P₍ P_ιn) * V/M„ where P₀ is the pressure in the gas supply line plus the pressure fall across the control valve as governed by the pressure regulator,

P_m is the maximum pressure to which the pressure vessel is to be pumped with odorant, V is the total inner volume of the pressure vessel, and

M₀ is the volume (amount) of liquid odorant, that during the latest emptying sequence of the pressure vessel is consumed and that is measured by integration of the signal from the odorant flow meter.

9. An arrangement according to claims 7 and 8, characterized by the feature that it comprises at least two pressure vessels for temporary storage of liquid odorant and that these by means of a valve arrangement are alternately connected for supply of odorant to the gas supply line and for refilling of inert gas and liquid odorant respectively, whereby there is no interuption in the supply of odorant to the gas supply line.

10. An arrangement according to claims 7, 8, and 9, characterized by the feature that it comprises pressure vessel(s) for temporary storage of liquid odorant that are approved for an operating pressure or 200 bar.