Abstract:
The invention relates to an examination process for replicating hydrate forming conditions in a gas pipeline and monitoring the effect of a low dosage hydrate inhibitor (LDHI) in suppressing hydrate formation at temperatures encountered in gas pipelines for dynamically determining LDHI feed rate for inhibition of hydrate formation comprising the steps of:
       diverting from a gas well a sample gas stream at a preselected rate;   introducing the diverted gas stream into a gas conduit through an inlet of the gas conduit;   feeding LDHI into the diverted gas stream at one or more predetermined rates to produce a LDHI-containing gas stream;   introducing the LDHI-containing gas stream into a coolable portion of the gas conduit, which coolable portion is provided with pressure sensors along the coolable portion;   cooling the LDHI-containing gas stream passing through the coolable portion of the gas conduit to a predetermined temperature; and   monitoring pressure of the LDHI-containing gas stream passing through the coolable portion of the gas conduit for a predetermined time range being at least as long as the gas residence time within the gas pipeline;   whereby a substantially uniform pressure drop along the coolable portion of the gas conduit during the predetermined time range indicates a LDHI feed rate sufficient to suppress hydrate formation at the predetermined temperature.

Description:
CROSS REFERENCE TO PRIOR APPLICATIONS 
     This application is a continuation-in-part of U.S. Ser. No. 14/919,060 filed on Oct. 21, 2015 and claims priority of Hungarian Patent Application No. P1500554 filed on Nov. 24, 2015, each of which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to an examination process for the in situ determination of rate of feeding an inhibitor into a gas pipeline for preventing hydrate formation. 
     BACKGROUND OF THE INVENTION 
     When transporting natural gas in a pipeline hydrates may form in the gas as the temperature of the gas decreases. During hydrate formation crystals are formed which can grow and agglomerate thereby forming hydrate plugs in the gas pipeline which hinder the gas transport thereafter. This problem is generally overcome on the one hand by heating the pipeline and on the other hand by feeding anti-hydrate compounds, typically thermodynamic inhibitors such as methanol, glycol or so called LDHI (Low Dosage Hydrate Inhibitor) type of inhibitors, into the pipeline that inhibit hydrate formation. The disadvantage of heating the pipeline is that it increases the cost of the transport of natural gas substantially. The use of methanol and other type of thermodynamic inhibitors is declining as these are strongly contaminating the environment, and require a substantially higher concentration than the LDHI type of inhibitors. Two types of LDHIs are known: the kinetic inhibitors, which decrease the speed of hydrate formation, and the anti-agglomerate inhibitors, which prevent agglomeration of the hydrate particles. In at least 95% of the cases the companies still employ the conventional, environmentally unfriendly methanol or glycol and expensive heating in order to protect gas pipes from hydrate plugs. Application of the environmentally friendly inhibitors is not yet wide-spread due to the higher expenses, although strong ecological interest is tied to it. The novelty of the present complex invention, in its details and as a whole, ensures the cost efficient and safe employment of inhibitors. 
     Hereinafter the LDHI type of inhibitors will be discussed, which will simply be referred to as LDHI or inhibitor for the sake of simplicity. 
     Inhibitors of different type and composition are available of which the selection of the most suitable inhibitor and its feeding rate depends on the various parameters of the gas well, the gas pipeline and the gas to be transported. Such parameters are for example the depth of the gas well, its yield, the natural gas condensate content, the stratum water content, and the carbon-dioxide content of the natural gas, the length and material quality of the pipeline, the flow parameters, the expected temperature conditions within the pipeline, etc. The suitable inhibitor is generally chosen by taking a sample from the gas well-head, transporting the sample to a remote laboratory where different inhibitors are added to the sample and measurements are performed in order to determine the efficiency of the inhibitor. The disadvantage of this method is that the composition of the gas sample and the ratio of the gas phase and liquid phase may change during transportation due to chemical reactions taking place inside the sample. A further disadvantage is that the amount of the sample does not allow for investigating hydrate formation at an industrial scale which may substantially influence the usability of the measurement results. 
     A great disadvantage of the currently employed inhibitor feeding systems is that regular on-site inspection is required for the continuous control of the reliability of operation. Furthermore, the feeding quantity can only be set on-site as well. In case of possible breakdown of operation or of a change of the environmental conditions (for example temperature) this system can only respond with big delay. 
     Presently, there is no known, complex, inhibitor feeding system and process using on-site measurements with the help of which the feeding of the rather expensive inhibitor into a gas pipeline could be optimized efficiently. The present solutions do not allow for determining the minimal quantity of inhibitor to be fed in, nor does it allow for early detection of a possible malfunction or breakdown of the feeding system. 
     It is an objective of the present invention to provide a process which overcomes the problems associated with the prior art. In particular, it is an objective of the invention to provide a process, which allows for the in situ determination of the rate of feeding an inhibitor into a gas pipeline for preventing hydrate formation, as well as remote control of the process of inhibitor feeding, thereby contributing to the spreading of the hydrate prevention technology that is based on the use of inhibitors. 
     SUMMARY OF THE INVENTION 
     The present invention comprises an examination process for replicating hydrate forming conditions in a gas pipeline and monitoring the effect of a low dosage hydrate inhibitor (LDHI) in suppressing hydrate formation at temperatures encountered in gas pipelines for dynamically determining LDHI feed rate for inhibition of hydrate formation. The process comprises the steps of:
         diverting from a gas well a sample gas stream at a preselected rate;   introducing the diverted gas stream into a gas conduit through an inlet of the gas conduit;   feeding LDHI into the diverted gas stream at one or more predetermined rates to produce a LDHI-containing gas stream;   introducing the LDHI-containing gas stream into a coolable portion of the gas conduit, which coolable portion is provided with pressure sensors along the coolable portion;   cooling the LDHI-containing gas stream passing through the coolable portion of the gas conduit to a predetermined temperature; and   monitoring pressure of the LDHI-containing gas stream passing through the coolable portion of the gas conduit for a predetermined time period;       

     whereby a substantially uniform pressure drop along the coolable portion of the gas conduit during the predetermined time period (observation time) indicates a LDHI feed rate sufficient to suppress hydrate formation at the predetermined temperature. 
     Preferably the preferred predetermined temperature to which the coolable portion is cooled is a temperature below hydrate formation temperature at gas pressures existing in a gas pipeline. The predetermined temperature is preferably between about 0° C. to about 16° C. 
     Gas observation time within the examined gas pipeline usually is in the range of about 1000 seconds to about 10000 seconds. Preferably, the predetermined observation time is at least twice the gas Residence Time within the coolable portion of the gas conduit. As used herein and in the appended claims, the term “Residence Time” means the time a particular gas molecule is within the coolable portion of the gas conduit and is calculated by a formula Residence Time equals volume of coolable portion of gas conduit divided by volumetric flow rate through the coolable portion of the gas conduit. 
     Preferably the process further includes the steps of providing an LDHI feeder comprising a telemetric data transmission system for the remote control and monitoring of the LDHI feeder; connecting the LDHI feeder to a feeding point of the gas pipeline; determining a temperature of the examined gas pipeline; and feeding the LDHI into the gas pipeline through the feeding point by the LDHI feeder at a LDHI feed rate sufficient to suppress hydrate formation at a temperature not exceeding the gas pipeline temperature. The gas pipeline temperature may be determined for example along the gas pipeline in the vicinity of the feeding point. 
     Certain advantageous embodiments of the invention are defined in the attached dependent claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a preferred embodiment of an industrial scale measuring system for preforming the process according to the invention. 
         FIG. 2 a    is a pressure difference diagram obtained in a measurement performed by the measuring system according to  FIG. 1 . 
         FIG. 2 b    is a temperature diagram obtained in a measurement performed by the measuring system according to  FIG. 1 . 
         FIG. 2 c    is a volume flow rate diagram obtained in a measurement performed by the measuring system according to  FIG. 1 . 
         FIG. 3  is a schematic diagram of a preferred embodiment of a laboratory scale measuring system for performing the process according to the invention. 
         FIG. 4  is a schematic diagram of an alternative laboratory scale measuring system. 
         FIG. 5 a    is a pressure difference diagram obtained in a measurement performed by the measuring system according to  FIG. 4 . 
         FIG. 5 b    is a temperature diagram obtained in a measurement performed by the measuring system according to  FIG. 4 . 
         FIG. 5 c    is a volume flow rate diagram obtained in a measurement performed by the measuring system according to  FIG. 4 . 
         FIG. 6  is a schematic diagram of an inhibitor feeding system provided with telemetric data transmission for performing the process according to the invention. 
         FIG. 7  is a schematic block diagram of a telemetric data transmission system of the inhibitor feeding system according to  FIG. 6 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A preferred embodiment of an industrial scale measuring system  200  of an examination system  100  for performing the process according to the invention can be seen in  FIG. 1 . The examination system  100  may advantageously comprise a laboratory scale measuring system  300  as well (see  FIG. 3 ). The main difference between the industrial scale measuring system  200  and the laboratory scale measuring system  300  is that the gas conduit  10  of the industrial scale measuring system  200  can be connected directly to the well-head of the gas well supplying the gas (natural gas) that is to be examined, whereby the examination may be performed in situ, i.e. on-site at the gas well. Furthermore, the dimensions of the industrial scale measuring system  200  are sufficiently close to the dimensions of the gas pipeline that is used to transport the gas from the gas well, in order to ensure that hydrodynamic and thermodynamic differences do not substantially influence the hydrate formation in the presence of the examined inhibitor. 
     In contradistinction, the purpose of the optional laboratory scale measuring system  300  is to allow pre-measurements on substantially smaller amounts of gas in order to reduce the number of inhibitors that are to be examined, it is thereby possible to pre-screen in a fast and cost-efficient way which one or more inhibitors should be examined in the industrial scale measuring system  200 . 
     The industrial scale measuring system  200  comprises a gas conduit  10  having a gas inlet  10 ′ which can be connected to a gas well-head. In the context of the invention the term gas well is understood to include any apparatus, formation or location serving as a gas source, for example a reservoir such as an underground reserve cave or artificial tank, and the term well-head is understood to refer to the gas outlet of such gas sources. The examination system  100  can be used in connection with any gas pipeline (either field conduit or pipes of a facility) or technology pipe in which hydrate formation may occur. Gas can be extracted from such gas pipelines as well, in this case the point of extraction (typically a conduit branch) is regarded as the gas well-head. The gas pipeline is connected to the gas well-head for transporting the gas to a gas collection station or any other place of designation. The purpose of the invention is to determine the required rate of feeding a suitable hydrate inhibitor into such a gas pipeline. The gas transported through the gas pipeline remains inside the gas pipeline (between the input and output locations) for a given residence time, thus the inhibitor and its feed-rate is generally considered adequate if it prevents hydrate formation during this residence time, preferably during twice the residence time. 
     The gas inlet  10 ′ of the gas conduit  10  is connectable to the well-head, preferably to the gate valve of the blind flange of the well-head assembly (Christmas-tree) or to an upper sample outlet of a conduit branch mounted on the gate valve in order to obtain dry gas free of liquid phase from the highest point of the gate valve. The gas inlet  10 ′ of the gas conduit  10  can be connected to the well-head either directly or indirectly (for example through an accessory part that is not part of the examination system  100 ). In the context of the present invention the gas inlet  10 ′ of the gas conduit  10  is regarded as being connectable to the gas well-head even if it is connectable indirectly, however, after connection continuous gas flow can be ensured from the gas well into the gas conduit  10 . 
     The gas conduit  10  is preferably formed as a pulse line. 
     The industrial scale measuring system  200  comprises a heat exchanger  12  and the gas conduit  10  comprises a coolable portion  11  which is arranged in the heat exchanger  12 . If necessary, the coolable portion  11  may also be heatable as well, thus the term coolable should not be interpreted in a limiting sense. 
     In the context of the present invention the terms “industrial scale” and “laboratory scale” relating to the measurement systems  200  and  300 , respectively, are used for distinguishing purposes only, and do not imply more restriction than if the measuring systems were called “first” and “second” measuring systems  200 ,  300 , respectively. However, it can be said that the dimensions (length, inner diameter) of the coolable portion  11  of the industrial scale measuring system  200  are greater than the dimensions of the corresponding coolable portion  111  (see  FIG. 3 ) of the laboratory scale measuring system  300 , preferably its length is at least two times greater, more preferably 5 to 15 times greater. The length of the coolable portion  11  of the industrial scale measuring system  200 , which serves for performing the measurements is preferably at least 100 m, and its inner diameter is at least 7 mm in order to be a sufficiently close approximation of the dimensions of the gas pipeline for rendering the modelling reliable. The dimensions of the coolable portion  111  of the laboratory scale measuring system  300  are smaller than this. 
     The coolable portion  11  of the industrial scale measuring system  200  is preferably formed as a coil pipe  11 ′ the inner diameter of which is chosen so as to avoid capillary effects, in order to ensure better resemblance of the measuring conditions to the hydrodynamic conditions inside the gas pipeline that is connected to the gas well-head. In order to avoid capillary effects the inner diameter is at least 7 mm, more preferably at least 10 mm. In order to reduce the necessary amount of natural gas for the measurement the inner diameter of the coil pipe  11 ′ is preferably not greater than 20 mm. The length of the coil pipe  11 ′ is preferably at least 100 m in order to ensure sufficient heat exchange surface for cooling purposes, and is preferably not more than 200 m, however, longer coil pipes  11 ′ may be used for the simulation of particularly long gas pipelines. 
     The material properties of the gas conduit  10  and in particular its coolable portion  11  are chosen in accordance with the material properties of the gas pipeline of the gas well in order to render the hydrodynamic and thermodynamic conditions more similar in this regard as well. Since the material of the gas pipelines used at gas wells is generally carbon steel, accordingly, preferably the gas conduit  10 , in particular the coil pipe  11 ′ that is arranged within a heat exchange space  14  of the heat exchanger  12 , is also made of carbon steel since it is preferred to have the same material properties as that of the gas pipeline in order to ensure that the same hydrodynamic conditions arise along the pipe wall. In case the material of the gas pipeline is acid-proof steel, this is preferably modeled by a coil pipe  11 ′ made of acid-proof steel. 
     The heat exchanger  12  preferably comprises a heat exchange space  14  wherein the coil pipe  11 ′ of the coolable portion  11  is arranged and which can be filled with a cooling medium. The heat exchanger  12  further comprises a tank  16  for discharging the cooling medium, a heat exchange unit  18  for cooling the cooling medium to a desired temperature and a deep freezer aggregator unit  20 . The aforesaid components of the heat exchanger  12  may be connected to each other for example according to the basic circuit diagram illustrated in  FIG. 1 , through ball valves  22 , and a pump  24  circulates the cooling liquid and helps to charge or discharge the heat exchange space  14  and the tank  16  of the heat exchanger  12 . Preferably, the liquid level within the tank  16  can be monitored for example by liquid level sensors and/or through a sight glass  26  shown in  FIG. 1 . 
     The industrial scale measuring system  200  preferably comprises an air heater  28  in connection with the heat exchange space  14  of the heat exchanger  12  for reheating the gas transported in the coil pipe  11 ′ in case of hydrate plug formation therein as will be explained in more detail later on. 
     Pressure measuring devices  30  are arranged at minimum two locations but preferably at four locations along the coolable portion  11  in order to determine the pressure difference between the consecutive locations. According to the present embodiment the pressure measuring devices  30  comprise a first pressure gauge  30 ′ and three differential pressure gauges  30   a ,  30   b ,  30   c  arranged downstream thereof, and the pressure is measured at the inlet of the coil pipe  11 ′, at ¼ of its length, at half of its length and at its outlet as illustrated in  FIG. 1 , whereby pressure difference can be measured at three different positions. In case of hydrate formation the location where the hydrate formation occurs can be deducted from the ensuing pressure difference. 
     The pressure gauge  30 ′ and the differential pressure gauges  30   a ,  30   b ,  30   c  are preferably in connection with a measurement controlling computer  32  such as to be able to transmit the measurement data to the computer  32 , which evaluates the received data with the help of a measurement controlling program. A data transmission connection between the pressure measuring devices  30  and the computer  32  can be ensured through wired or wireless connection (e.g. WiFi connection) as is known per se. In the context of the present invention the term computer is used in a broad sense including any hardware device that is suitable for collecting and processing data and, based thereon, controlling units of the examination system  300 , for example desk top computer, laptop, tablet, smart phone, microcontroller, etc. The computer  32  preferably comprises one or more input devices (for example keyboard  34 , mouse  36 , etc.), one or more output devices (for example display  38 , printer, etc.) and may comprise interfaces that can serve as both input and output devices (for example touch screen, CD/DVD reader/writer, etc.). 
     Preferably, thermometers  40   a ,  40   b  and  40   c  are connected to the coolable portion  11  of the gas conduit  10  of the industrial scale measuring system  200  for measuring the temperature of the gas transported within the coil pipe  11 ′ at minimum two locations but preferably at three locations and a forth thermometer  40 ′ is provided for measuring the temperature of the cooling liquid. The thermometers  40   a ,  40   b ,  40   c  and  40 ′ preferably transmit the measurement data to the computer  32 . 
     The industrial scale measuring system  200  preferably further comprises an inhibitor feeding system  42  which is connected to the gas conduit  10  between the gas inlet  10 ′ and the coolable portion  11 . The inhibitor feeding system  42  comprises an inhibitor tank  44  and a feeding pump  46 , preferably an electric feeding pump connected therewith, which may be connected to the gas conduit  10  for example through ball valve  47  and check valve  48  as illustrated in  FIG. 1 . Preferably a pressure gauge  49  is provided between the feeding pump  46  and the ball valve  47 . 
     The gas (natural gas) transported through the gas pipeline from the gas well comprises liquid phase stratum water and/or natural gas condensate in the amount characteristic of the gas well, the presence of which may influence the hydrate formation and the formation of hydrate plugs. The inventor has recognized that the amount of the stratum water and natural gas condensate that can be measured in the gas pipeline does not necessarily correspond to the proportions present in the gas conduit  10  of the industrial scale measuring system  200 , for which reason it is preferred to separate the liquid phase (and any solid contaminants) from the examined gas by a separator  50 , and feed stratum water and natural gas condensate in the proportions measurable in the transport pipeline into the gas conduit  10  upstream of the coolable portion  11 . The industrial scale measuring system  200  preferably comprises for this purpose a stratum water feeding system  52  and a natural gas condensate feeding system  62  both of which are connected to the gas conduit  10  between the separator  50  and the coolable portion  11 . 
     The stratum water feeding system  52  comprises a stratum water tank  54  and a feeding pump  56 , preferably a pneumatic feeding pump, connected therewith, which may be connected to the gas conduit  10  for example through a ball valve  57  and check valve  58  as illustrated in  FIG. 1 . Preferably a pressure gauge  59  is provided between the feeding pump  56  and the ball valve  57 . 
     Similarly, the natural gas condensate feeding system  62  comprises a natural gas condensate tank  64  and a feeding pump  66 , preferably a pneumatic feeding pump, connected therewith, which may be connected to the gas conduit  10  for example through a ball valve  67  and check valve  68  as illustrated in  FIG. 1 . Preferably a pressure gauge  69  is provided between the feeding pump  66  and the ball valve  67 . 
     The three feeding systems  42 ,  52 ,  62  can be formed as a single integrated system. 
     The separator  50  can be any kind of known device suitable for separating liquid. Preferably, a tank  51  is connected to the separator  50  through a ball valve  70  for collecting the separated liquid and solid contaminants. The gas inlet  10 ′ is preferably separated from the separator  50  by a ball valve  72 . 
     Similarly, a separator  50 ′ can be applied downstream of the coolable portion  11  of the gas conduit  10  in order to separate the natural gas condensate, stratum water and inhibitor that has been fed into the gas stream. Preferably, a tank  51 ′ is also connected to the separator  50 ′ through a ball valve  70 ′. Preferably, the separator  50 ′ is connected to the portion of the gas conduit  10  exiting the heat exchanger  12  through a ball valve  74 . 
     If the gas inlet  10 ′ of the gas conduit  10  is connected to the gas well, a pressure regulator  80  is preferably connected to the gas conduit  10  downstream of the separator  50  following the gas inlet  10 ′ because the pressure at the gas well is generally somewhat higher than within the gas pipeline and the pressure regulator  80  serves to reduce the pressure of the transported gas in order to reproduce the pressure conditions within the gas transport pipeline connected to the gas well. It is also possible to connect the gas inlet  10 ′ of the gas conduit  10  to a notch on the gas pipeline in which case the pressure regulator  80  is not required. 
     According to a preferred embodiment the pressure regulator  80  comprises a pressure reducing valve  82  and pressure gauges  84  and  86  connected upstream and downstream thereof, in order to visually present the entry and exit pressure values. The measurement data of the pressure gauges  84  and  86  can be transmitted to the computer  32 , which may control the pressure reducing valve  82 . The pressure regulator  80  is preferably connected to the coil pipe  11 ′ of the coolable portion  11  through a check valve  88 . 
     A further pressure regulator  90  may be provided upstream of the gas outlet  10 ″ of the gas conduit  10  for setting the pressure of the gas exiting the gas conduit  10 . According to a preferred embodiment the pressure regulator  90  comprises a pressure reducing valve  92  and pressure gauges  94  and  96  connected upstream and downstream thereof, in order to visually present the entry and exit pressure values. The pressure regulator  90  is preferably connected to the separator  50 ′ through a check valve  98 . 
     The pressure regulator  90  is preferably followed by a choke valve  102  for setting the flow rate of the gas inside the gas conduit  10  which can be measured by a flowmeter  104 . The flowmeter  104  may transmit measurement data to the computer  32  over a data transmission connection therewith. The pressure regulator  90 , the choke valve  102  and the flowmeter  104  are preferably protected from any solid or liquid contaminants that may eventually pass the separator  50 ′ by a filter  99 . 
     Preferably a conduit  106  for introducing hot water, a conduit  107  for introducing air and/or a conduit  108  for introducing nitrogen is connected to the gas conduit  10  of the industrial scale measuring system  200  between the gas inlet  10 ′ and the coolable portion  11  through ball valves  105   a ,  105   b ,  105   c  respectively. The hot water conduit  106  is advantageously connected to the local hot water network or it may be connected to the cold water network with the interposition of a water heater. The nitrogen is preferably introduced into the conduit  108  from a nitrogen tank  109 . 
     The examination system  100  comprising the industrial scale measuring system  200  and optionally the laboratory scale measuring system  300  is preferably formed as a mobile station, whereby it can be transported to the location of the gas well, which is to be examined, and the measurements can be performed there. The examination system  100  is preferably provided in a container, thus the measuring apparatuses and accessories located in the container can be easily installed on the site of the examined well, whereby the measurements for preventing hydrate formation can be performed substantially faster and more efficiently, furthermore, the problems associated with the transport of the gas sample can be eliminated. Further advantage of the local (in situ) measurements is that the different stratum water and natural gas condensate content of the well flow can be easily taken into account by feeding the stratum water and natural gas condensate obtained from the well into the examination system  100 . Since the efficiency of the examinations depend considerably on the number of measurements, hence the in situ performance of a high number of measurements can substantially reduce the time required to analyze a gas well; whereas the conventional measurements performed in laboratories inside remote buildings required months, the same measurements may be performed within a week with the help of the mobile station. 
     The inner space of the container is preferably monitored with a gas detector (not shown) in order to eliminate the risk of a gas explosion, which detector signals at 10% of LEL (Lower Explosive Limit), turns a ventilation fan on at 20% of LEL, and shuts off the electric system at 30% of LEL. 
     The energy source of the mobile examination system  100  is preferably a current generator. 
     The industrial scale measuring system  200  is applied as follows. 
     According to a first step of the process according to the invention the quantity of the inhibitor that is to be fed into the gas pipeline is determined with the help of the industrial scale measuring system  200 . Before starting the measurements the tank  16  of the heat exchanger  12  is filled with a cooling liquid, for example a 3:1 ratio mixture of glycol to distillated water, through the ball valve  22 . 
     At the start of the measurement the heat exchange space  14  is filled with the cooling liquid from the tank  16  with the help of the pump  24 . The cooling liquid is continuously circulated in the heat exchange space  14  by the deep freezer aggregator unit  20  which is thereby cooled to the desired temperature. The flow can be monitored through the sight glass  26 . 
     The natural gas to be examined is obtained from the well, through the conduit branch of the well head, which is then transported through a pulse line to the gas inlet  10 ′ of the gas conduit  10  of the measuring system  200 . The natural gas enters the industrial scale measuring system  200  through the ball valve  72  arranged at the gas inlet  10 ′. The liquid phase (practically stratum water and natural gas condensate) and solid contaminants are separated from the introduced natural gas with the help of the separator  50 . 
     The required pressure for the measurement is then set by the pressure regulator  80 . 
     In order to examine the formation of hydrates the conditions within the gas pipeline have to be modeled. This is done by determining the amount of stratum water and natural gas condensate carried in the gas pipeline and a corresponding amount of stratum water and natural gas condensate is fed into the gas conduit  10  after the liquid phase has been separated but upstream of the entrance of the coolable portion  11 . The amounts to be fed into the gas conduit  10  can be determined based on data of prior measurements (possibly conducted by third parties). 
     The feeding of the inhibitor, stratum water and natural gas condensate is ensured by the feeding systems  42 ,  52 ,  62  such that the inhibitor, stratum water and natural gas condensate are fed into the gas conduit  10  from the tank  44 ,  54 ,  64  of each feeding system  42 ,  52 ,  62  by the electric or pneumatic feeding pumps  46 ,  56 ,  66 , respectively. The feed rate of the inhibitor is set in accordance with the examination (such an examination may be for example whether or not a given mass flow of a given inhibitor is sufficient to prevent hydrate formation at a given temperature). The stratum water and the natural gas condensate are fed into the natural gas at the amount necessary to obtain a composition ratio corresponding to the composition ratio within the natural gas transported inside the gas pipeline. 
     The gas containing the added inhibitor, stratum water and natural gas condensate is transported to the coolable portion  11  of the gas conduit  10 , which is arranged inside the heat exchange space  14  of the heat exchanger  12 , where the gas is cooled to a predetermined temperature with the cooling liquid. In the context of the present invention the predetermined temperature to which the gas is cooled is the lowest temperature reached by the gas stream in the coolable portion  11 . When using the heat exchanger  12  the theoretical minimum for the gas temperature is the temperature of the cooling liquid. In practice the temperature of the cooling liquid can be regarded as the predetermined temperature. The temperature is measured continuously at four locations (at the inlet and outlet of the coil pipe  11 , at ¼ of its length, furthermore the temperature of the cooling liquid is measured) by the thermometers  40   a ,  40   b ,  40   c  and  40 ′. 
     The drop of pressure of the natural gas within the heat exchange space  14  is measured at three locations by the pressure measuring devices  30  as explained earlier, and it is determined from the measured pressure difference whether or not a hydrate plug was formed along the measured portion, which hydrate plug obstructs the flow and thereby increases the pressure. 
     The resulting pressure drop values and temperature data are transmitted to the computer  32  controlling the measurement, which then processes the data and preferably displays the data on the display  38 . The computer  32  uses the data to determine the result of gas hydrate formation in connection with the gas obtained from the given gas well. The computer  32  preferably also monitors the measurement data of the pressure gauges  49 ,  59 ,  69  belonging to the feeding pumps  46 ,  56 ,  66 , and may control the controllable elements thereof based on the measurement data. 
     The analysis performed by the examination system  100  helps in operating an inhibitor feeder  290  installed permanently at the given well with the best efficiency. The most efficient industrial inhibitor can be selected and the quantity of the inhibitor applied at the well can be reduced. 
     After examination, the natural gas is freed from the added stratum water, natural gas condensate and eventually any solid contaminants by the separator  50 ′ and the filter  99 , and after having passed the flowmeter  104  it is conducted out from the container. The desired flow rate is set by the choke valve  102  having regard to the feed-back of the flowmeter  104 . 
     After the system freezes, i.e. after a hydrate plug is formed, the coil pipe  11 ′ arranged within the heat exchanger  12  has to be heated in order to eliminate the hydrate plug. The heating is performed by discharging the cooling medium from the heat exchange space  14  of the heat exchanger  12  into the tank  16 , after which the coil pipe  11 ′ is heated by the air heater  28  by blowing in air of approx. 40-50° C. until the plug is dissolved. The cooling medium is pumped back into the heat exchange space  14  from the tank  16 , whereby substantially less time and energy is required for obtaining the necessary cooling temperature as compared to the case where the cooling medium is heated in the heat exchange space  14  for eliminating the hydrate plug. 
     The examination of the hydrate formation is performed by the industrial scale measuring system  200  for more than one type of inhibitors and/or more than one feed rate and/or by cooling the gas to more than one temperature. After each measurement the cooling medium is discharged into the tank  16 , then the system is washed with hot water coming through the conduit  106 , finally nitrogen is blown through the system, which is introduced from the tank  109  through the conduit  108 . It is also possible to mix an inhibitor-neutral cleaning agent to the hot water. 
     The industrial scale measuring system  200  according to  FIG. 1  has been built and the results of measurements performed therewith can be seen in  FIGS. 2 a -2 c    and will be discussed hereinafter. 
     EXAMPLES 
     Example 1 
     The length of the coil pipe  11 ′ of the built measuring system  200  was 160 m, its inner diameter was 10 mm. The volume flow rate of the natural gas was set to 150 l/min with the help of the pressure regulator  90 , which value was measured at normal atmospheric pressure. The gas was freed from stratum water, natural gas condensate and solid contaminants and into this gas stream stratum water was fed at a rate of 14 ml/min, and natural gas condensate was fed at a rate of 14 ml/min by the stratum water feeding system  52  and the natural gas condensate feeding system  62 , respectively. An inhibitor formed as the 1:1 ratio mixture of anti-agglomerate type GH-86 LDHI concentrate (sold by MOL-LUB Ltd., Almásfüzitö, Hungary) and natural gas condensate was fed into the gas conduit  10  at a rate of 0.29 ml/min with the help of the feeding system  42 . 
     The temperature of the cooling liquid within the heat exchange space  14  of the heat exchanger  12  was 2° C., which was continuously monitored by the thermometer  40 ′. The measurement is preferably performed for 1.5 times longer than the Residence Time of the natural gas inside the measured gas conduit. In the present case the measurement was only performed for 4000 sec. 
     The pressure differences measured by the differential pressure gauges  30   a ,  30   b  and  30   c  are plotted against time in  FIG. 2 a   . As can be seen the differential pressure gauges  30   a  and  30   b  measured about 0 bar value during the whole time, while the pressure difference measured by the differential pressure gauge  30   c  suddenly increased around 2000 sec, then it fluctuated strongly and finally reached its upper measuring limit at about 4000 sec. From this it can be concluded that at 2° C. after 2000 sec the delivered inhibitor is no longer able to prevent gas hydrate formation, as a consequence gas hydrate starts to form along the inner surface of the coil pipe  11 ′, whereby the penetrable cross-section decreases, which leads to a pressure difference. The pressure difference fluctuation is due to the fact that the gas flow is often able to wash away the hydrate particles from the pipe wall, whereby the pressure difference is eliminated or reduced along the given pipe portion. It can also be concluded from the measurement data provided by the differential pressure gauges  30   a ,  30   b ,  30   c , that gas hydrate formation occurred beyond the middle point of the coil pipe  11 ′, since the third differential pressure gauge  30   c  measured substantial pressure difference. The sudden increase of pressure difference at about 4000 sec indicates the formation of a hydrate plug, the coil pipe  11 ′ becomes impenetrable to a great extent, whereby the pressure difference drastically increases between the two sides of the hydrate plug. 
     The temperatures measured by the thermometers  40   a ,  40   b ,  40   c  are plotted against time in  FIG. 2 b   . The first thermometer  40   a  measures the temperature at the inlet of the coil pipe  11 ′ where the cooling liquid that is circulated in the heat exchange space  14  has not yet cooled the gas, thus this temperature is substantially higher. The second thermometer  40   b  is arranged at the third of the coil pipe  11 ′, while the third thermometer  40   c  is arranged in the vicinity of the outlet. The third thermometer  40   c  should measure approximately the same but always somewhat lower temperature than the second thermometer  40   b , however, as can be seen, after about 2000 sec the temperature measured by the third thermometer  40   c  started to increase and surpassed the temperature measured by the second thermometer  40   b , although the temperature along the coil pipe  11 ′ should be closer and closer to the 2° C. temperature of the cooling liquid. The deviation is due to the fact that the hydrate formation is an exoterm process, meaning that it is accompanied by heat production, whereby the temperature increases along the pipe portion where gas hydrate starts to form. This phenomenon allows for deducting gas hydrate formation from the temperature measurement. 
       FIG. 2 c    shows the volume flow rate measured by the flowmeter  104  at normal atmospheric pressure and is plotted against time. The measurement data delivered by the flowmeter  104  also allows for determining whether or not hydrate formation occurred because, due to the hydrate deposition, the volume flow rate of the gas temporarily decreases, then it is compensated as can be seen in  FIG. 2 c   . Naturally, in case the system freezes, i.e. when such hydrate plug is formed which seals off the coil pipe  11 ′ completely, then the volume flow rate drops to zero. 
     The process allows for examining whether or not gas hydrate is formed inside the coolable portion  11  of the gas conduit  10  when changing the type and feed rate of the inhibitor and the temperature of the cooling liquid. The measurement is performed for at least as long as the natural gas would dwell (travel) inside the gas pipeline, whereby it is possible to experimentally model whether or not gas hydrate would form inside the gas pipeline at the given temperature and in the presence of the given inhibitor. Since the objective of the invention is to reliably prevent gas hydrate formation, thus it is expedient to measure for a longer period than the residence time of the gas when transported along the gas pipeline. It has been found that it is advantageous to measure for a time period of at least 1.5 times the residence time of the natural gas transported within the gas pipeline, in this way the inhibitor quantity (concentration) that is deemed sufficient in the course of the measurement has been found adequate in practice to prevent hydrate plug formation along the whole length of the gas pipeline, while it does not result in feeding an excessive amount of inhibitor into the gas pipeline. 
     The examination system  100  preferably also comprises a laboratory scale measuring system  300  (see  FIG. 3 ) in addition to the industrial scale measuring system  200 , which allows for faster and less expensive pre-measurements performed with a smaller quantity of gas in order to pre-screen the possible inhibitors. 
     The components of the laboratory scale measuring system  300  are similar to that of the industrial scale measuring system  200 , for which reason the following description of the laboratory scale measuring system  300  concentrates mainly on the differences. 
     A gas inlet  110 ′ of a gas conduit  110  of the laboratory scale measuring system  300  transporting the examined gas (natural gas) is preferably connected to the gas well-head, or to a conduit branch attached thereto, or to a gas bottle  113  containing a gas sample from which stratum water and natural gas condensate have been separated. The gas bottle  113  can be preferably a commercially available bottle of standard size and pressure range. 
     The pressure of the gas introduced into the gas conduit  110  can be set to the value required for the examination by a pressure regulator  180 . The pressure regulator  180  preferably comprises a pressure reducing valve  182  and pressure gauges  184  and  186  connected upstream and downstream thereof, which can be connected to the same computer  32  as the measuring devices of the industrial scale measuring system  200 . It should be appreciated that preferably all measuring devices of the laboratory scale measuring system  300  may be connected to the same computer  32  or to another computer of similar function through wired or wireless connection allowing for data transmission. 
     The pressure regulator  180  is preferably connected to a coolable portion  111  of the gas conduit  110 , that is formed as a measuring cell  111 ′ and is arranged within a heat exchange space  114  of a heat exchanger  112 , through a two-way valve  172 . A container  116  is connected to the heat exchange space  114  for discharging the cooling agent therein. 
     A liquid cooler  118  is connected to the heat exchange space  114  of the heat exchanger  112  for cooling the cooling liquid with any known technology. 
     The cooling liquid that has been cooled to the desired temperature is preferably introduced into the heat exchange space  114  of the heat exchanger  112  from the liquid cooler  118 . 
     The measuring cell  111 ′ is also a pipe, the dimensions of which are chosen such as to allow for fast and cost efficient measurements, i.e. the gas and inhibitor are used in small amounts. Accordingly, the inner diameter of the measuring cell  111 ′ is between 3 mm and 5 mm, preferably approx. 4 mm; its outer diameter is approx. 6 mm; its length is preferably not more than 50 m, more preferably not more than 30 m, for example approx. 20 m. The measuring cell  111 ′ may optionally have a two-part structure: for example it can be made up of a 6 m long portion and a 12 m long portion, and a pressure gauge and thermometer can be arranged between the two portions. 
     The gas conduit  110 , in particular the measuring cell  111 ′ arranged in the heat exchange space  114  of the heat exchanger  112  is preferably made of carbon-steel, or acid-proof steel in case the gas pipeline is made of acid-proof steel as explained in connection with the industrial scale measuring system  200 . 
     Pressure measuring devices  130  are arranged at minimum two locations but preferably at three locations along the coolable portion  111  in order to determine the pressure difference between the consecutive locations. According to the present embodiment the pressure measuring devices  130  are differential pressure gauges  130   a  and  13   b  and the pressure is measured at the inlet of the coil pipe  111 ′, at ⅓ of its length, and at its outlet, whereby pressure difference can be measured at two different positions. In case of hydrate formation the location where the hydrate formation occurs can be deducted from the ensuing pressure difference. 
     Preferably, thermometers  140  are connected to the coolable portion  111  of the gas conduit  110  for measuring the temperature of the gas transported within the measuring cell  111 ′ at minimum two locations but preferably at three locations by three thermometers  140   a ,  140   b ,  140   c  and a forth thermometer  140 ′ is provided for measuring the temperature of the cooling liquid. The thermometers  140   a ,  140   b ,  140   c ,  140 ′ preferably transmit the measurement data to the computer  32 . 
     The laboratory scale measuring system  300  preferably further comprises an inhibitor feeding system  142 , which is connected to the gas conduit  110  upstream of the coolable portion  111 . The inhibitor feeding system  142  comprises an inhibitor tank  144  and a feeding pump  146 , preferably an electric feeding pump connected therewith, which may be connected to the gas conduit  110  for example through a two-way valve  147  and a floating piston cell  148  as illustrated in  FIG. 3 . The floating piston cell  148  serves to inject the hydrate inhibitor into the gas. Preferably a pressure gauge  149  is provided between the feeding pump  146  and the ball valve  147 . 
     The liquid phase and any solid contaminants have been preferably separated in advance from the gas sample used in the laboratory scale measuring system  300 , or these are separated in a separator installed at the gas well. Stratum water and natural gas condensate are fed into the gas conduit  110  upstream of the coolable portion  111  in the amount characteristic for the gas well. The natural gas condensate is preferably mixed with the inhibitor, and injected into the gas conduit  110  by the inhibitor feeding system  142 , while a separate stratum water feeding system  152  is used for adding the stratum water. It is also conceivable to provide a separate feeding system for the natural gas condensate. The stratum water feeding system  152  comprises a stratum water tank  154  and a feeding pump  156 , preferably an electric feeding pump. Preferably a pressure gauge  159  is provided between the feeding pump  156  and the inlet of the inhibitor feeding system  142 . 
     The measurement data of the pressure gauges  149 ,  159  are preferably also transmitted to the computer  32 , which may optionally control the feeding systems  142 ,  152  using this data. 
     Preferably, a separator  150 ′ is applied downstream of the coolable portion  111  of the gas conduit  110  for the deposition of the liquids condensed from the gas flow, primarily for the separation of the natural gas condensate, stratum water and inhibitor that has been fed into the gas stream. Preferably, a tank  151 ′ is also connected to the separator  150 ′ through a two-way valve  170 ′. Preferably, the separator  150 ′ is connected to the portion of the gas conduit  110  exiting the heat exchanger  112  through a three-way valve  174 . The three-way valve  174  allows for discharging into the tank  121  a washing liquid that is passed through the gas conduit  110  when it is being washed. The tank  121  is preferably connected to the inhibitor feeding system  142  through a valve  175  as can be seen in  FIG. 3 . 
     A pressure regulator  190  is preferably provided upstream of the gas outlet  110 ″ of the gas conduit  110  for setting the pressure of the gas exiting the gas conduit  110 . According to a preferred embodiment the pressure regulator  190  comprises a pressure reducing valve  192  and pressure gauges  194  and  196  connected upstream and downstream thereof, in order to visually present the entry and exit pressure values. The measurement data of the pressure gauges  194 ,  196  may be transmitted to the computer  32 . The pressure regulator  190  is preferably connected to the separator  150 ′ through a filter  199 . 
     The pressure regulator  190  is preferably followed by a choke valve  202  and a flowmeter (mass flow meter)  204  for setting the flow rate of the gas inside the gas conduit  110 . The flowmeter  204 , just like the other measuring devices, may transmit measurement data to the computer  32  over a data transmission connection therewith. The flowmeter  204  is preferably protected from any solid or liquid contaminants that may eventually pass the separator  150 ′ by a filter  199 . 
     Preferably a conduit  206  for introducing hot water, a conduit  207  for introducing air and a conduit  208  for introducing chemical agents is connected to the gas conduit  110  of the laboratory scale measuring system  300  upstream of the coolable portion  111  through subsequent magnetic valves  211   a ,  211   b  and two-way valves  212   a ,  212   b , respectively, as can be seen in  FIG. 3 . The magnetic valves  211   a ,  211   b  are preferably also controlled by the computer  32 , and compressed air and washing water are introduced into the gas conduit  110  through these valves  211   a ,  211   b  when the gas conduit  110  is being cleaned. 
     The hot water conduit  206  is preferably connected to the local cold water network. The cold water is pumped to a water heater  215  connected to the conduit  206  by a pump  214 . The water heater  215  heats the cold water by a heating body  215   a  and stores the hot water in a tank  215   b  or the hot water is provided as it runs through the heating body  215   a  without being stored. The water temperature can be set by a temperature regulator  213  manually or optionally by the computer  32 . Another possibility is to connect the hot water conduit  206  to the hot water network. 
     Preferably, the chemical agent is introduced into the conduit  208  from a tank  209 , and the conduit  208  can be closed off by a separate valve  210 . 
     Preferably a compressor  216  is connected to the air introducing conduit  207  for venting and drying the gas conduit  110  between the measurements. The compressor  216  can be any known device, for example a device providing maximum 6-8 bar pressure. The compressor  216  typically comprises an air tank  220 . 
     The laboratory scale measuring system  300  is applied as follows. 
     The examined natural gas is introduced into the gas conduit  110 . The natural gas passes the pressure regulator  180  before entering the coolable portion  111  of the gas conduit  110  that is arranged in the heat exchanger  112 . The valves  212   a  and  212   b  are kept closed during the measurement. 
     The examined gas is introduced into the coolable portion  111  through the valve  172 . The hydrate inhibitor needs to be mixed to the examined gas in advance, which can be accomplished by the feeding pump  142  in accordance with the pre-set feeding rate. The inhibitor is stored in the tank  144  together with the required amount of natural gas condensate before starting the measurement. 
     The stratum water must also be ensured for the measurements, which can be fed from the tank  154  by the feeding system  152 . 
     The heat exchange space  114  of the heat exchanger  112  is cooled to the extent required for the measurement by the cooling liquid provided by the liquid cooler  118 . The measuring cell  111 ′ of the coolable portion  111  of the gas conduit  110 , made up of two portions, is arranged inside the heat exchange space  114 . 
     The pressure drop is measured between three locations within the measuring cell  111  by the differential pressure gauges  130   a  and  130   b  as explained earlier, and the measurement data is collected by the computer  32  for the purpose of determining hydrate formation. The temperature is measured at the inlet and outlet of the measuring cell  111 ′ and between the two portions of the measuring cell  111 ′, furthermore, the temperature of the cooling medium is also measured inside the heat exchange space  114 , and the data is transmitted to the computer  32 . 
     Downstream of the coolable portion  111  the gas can be conducted, through the three-way valve  174 , to the separator  150 ′ and then to the filter  199  in order to separate the stratum water, natural gas condensate and solid contaminants. The gas flows from the filter  199  to the pressure regulator  190  from where it flows to the choke valve  202  and the flowmeter  204 . The choke valve  202  has a high resolution fine regulator with which the desired flow parameters can be set, which are measured by the flowmeter  204 . 
     The examined gas exits the measuring system  300  through the gas outlet  110 ″, and exits the container. 
     Hydrate formation is also examined by the laboratory scale measuring system  300  in different quantities 
     The examination of the hydrate formation is performed by the laboratory scale measuring system  300  for an inhibitor added in different quantities and/or more than one type of inhibitors and/or at least at two given temperatures. Typically more than one type of commercially available inhibitors are examined in order to measure only those types in the industrial scale measuring system  200  which could be efficient according to the laboratory measurements. 
     After each measurement the gas conduit  110  is washed with hot water and chemicals, and high pressure air is blown through the system. The water required for the washing phase is obtained from the water heater  215 , which is connected to the pump  214  that is connected to the cold water network. The water heated by the heating body  215   a  and stored in the tank  215   b  of the water heater  215  is introduced into the gas conduit  110  through the conduit  206 . Naturally, the water heater may be a continuous flow water heater, in which case the water only dwells temporarily inside the tank  215   b , while it is being heated. 
     In case of hydrate formation the cooling liquid is preferably discharged from the heat exchange space  114  into the container  116 , after which the gas conduit  110  is washed. For this, chemicals are added to the hot water from the tank  209  through the conduit  208  and the valve  210 . 
     The washing liquid enters the measuring cell  111 ′ through the magnetic valve  211   a  and the valve  212   a . During washing the valve  172  must be closed and the three-way valve  174  is set such that the washing liquid flows into the tank  121 . The valve  212   b  must be closed during the washing phase. 
     The drying phase following the washing phase is preferably performed by the air introduced through conduit  207 , the pressure of which is set by the compressor  216 . The pressure is preferably about 30 bar. The air can be introduced into the measuring cell  111 ′ through the magnetic valve  211   b  and the valve  212   b . When blowing-off the air the three-way valve  174  is set to its measurement state, in which state the air exits the system through the natural gas outlet and is lead outside of the container. 
     The construction of the laboratory scale measuring system  300 , serving to examine the formation of hydrates and the performance of hydrate inhibiting preparations, is such that it can be easily arranged within a container and it can be transported without risk of failure. The devices and accessory components are also sufficiently secured. 
       FIG. 4  shows another exemplary embodiment of the laboratory scale measuring system  300 ′ according to the invention. For the sake of simplicity only the differences will be discussed in detail with regard to the previously presented laboratory scale measuring system  300 . Same components are indicated with the same reference signs. 
     According to this embodiment the gas that is used for the measurement is extracted from the gas pipeline transporting the natural gas or from the well head as explained in connection with the industrial scale measuring system  200 . The extracted gas preferably enters the gas conduit  110  of the laboratory scale measuring system  300 ′ through valve  230 . 
     According to the present embodiment the natural gas condensate is not mixed with the inhibitor, thus a separate inhibitor feeding system  142  is provided for delivering the inhibitor and a separate natural gas condensate feeding system  162  is provided for delivering the natural gas condensate into the gas conduit  110 . The inhibitor feeding system  142  comprises, in this case as well, an inhibitor container  144  and a feeding pump  146  connected therewith. Similarly, the natural gas condensate feeding system  162  comprises a natural gas condensate container  164  and a feeding pump  166 , preferably an electric feeding pump, connected therewith. 
     The inhibitor feeding system  142 , the stratum water feeding system  152  and the natural gas condensate feeding system  162  are preferable connected to the gas conduit  110  upstream of the pressure gauge  159  through valves  143 ,  153 ,  163 . 
     A container  116  is connected to the heat exchange space  114  of the heat exchanger  112  for discharging the cooling agent, as well as a liquid cooler  118  for cooling the cooling liquid by any known technology. 
     According to the present embodiment it is possible to allow the natural gas to exit through conduit  250  and valve  252  downstream of the separator  150  when it is not required to measure with the flowmeter  204 , for example because the measurement has ended. 
     A further difference is, that according to this embodiment the gas conduit  110  is blown through with nitrogen gas after finishing the measurement instead of washing it with a chemical agent and blowing hot air through it. The nitrogen gas is introduced into the gas conduit  110  from a nitrogen bottle  260  through a valve  262 , and it is first discharged through the conduit  250  and then through the gas outlet  110 ″. 
     The possibility of employing chemical washing may be retained in this case as well. Liquid containing chemicals may be delivered through the valve  210 , for example such that it is possible to connect a tank  209  containing the chemical liquid to the valve  210 . In this case a tank  121 ′ may be connected to the three-way valve  174  for collecting the chemical liquid, preferably as indicated in  FIG. 4 , through a valve  271 . 
     The course of the measurement performed with the measuring system  300 ′ according to  FIG. 4  is very similar to that of the measuring system  300  depicted in  FIG. 3 . 
     The natural gas condensate and the stratum water and possibly any solid contaminants are preferably separated from the natural gas obtained from the gas pipeline before it is introduced into the gas conduit  110  through the valve  230 . The pressure of the introduced natural gas is set by the pressure regulator  180 , after which the examined inhibitor is fed into the gas conduit  110  with the inhibitor feeding system  142 , as well as stratum water and natural gas condensate, in the proportions corresponding to that within the gas pipeline, with the stratum water feeding system  152  and the natural gas condensate feeding system  162 . The mixture is delivered into the measuring cell  111 ′ arranged in the heat exchange space  114  of the heat exchanger  112  where it is cooled by the cooling liquid within the heat exchange space  114 . Any hydrate formation and its location are determined from the temperatures measured by the thermometers  140   a ,  140   b ,  140   c  and from the pressure differences measured by the differential pressure gauges  130   a ,  130   b.    
     The natural gas, inhibitor, stratum water, natural gas condensate mixture, once it exits the measuring cell  111 ′ is introduced into the separator  150  in order to separate the stratum water, natural gas condensate and solid contaminants. After this, the gas is led through the filter  199 , then it passes the pressure regulator  190  and the choke valve  202  before it enters the flowmeter  204 . The measurement data of the flowmeter  204  can also be used as an indicator of the possible presence of gas hydrates. 
     The measuring system  300 ′ according to  FIG. 4  has been built and the results of measurements performed with the measuring system  300 ′ are shown in  FIGS. 5 a -5 c    and are discussed hereinafter. 
     Example 2 
     The length of the measuring cell  111 ′ of the built measuring system  300 ′ was 18 m, its inner diameter was 4 mm. The volume flow rate of the natural gas was set to 15 l/min with the help of the pressure regulator  190 , which value was measured at normal atmospheric pressure. The gas was freed from stratum water, natural gas condensate and solid contaminants and into this gas stream stratum water was fed at a rate of 1 ml/min, and natural gas condensate was fed also at a rate of 1 ml/min by the stratum water feeding system  152  and the natural gas condensate feeding system  162 , respectively. An inhibitor formed as the 1:1 ratio mixture of anti-agglomerate type GH-86 LDHI concentrate (sold by MOL-LUB Ltd., Hungary) and natural gas condensate was fed into the gas conduit  10  at a rate of 0.014 ml/min with the help of the feeding system  142 . 
     The temperature of the cooling liquid within the heat exchange space  114  of the heat exchanger  112  was 4° C., which was continuously monitored by the thermometer  140 ′. The measurement performed with the laboratory scale measuring system  300 ′ has the informative purpose of pre-screening the inhibitors, hence it is not an objective here to simulate the gas transport along the whole length of the gas pipeline. Accordingly, the measurement is performed for a shorter period of time. It has been found that it is practical to measure during 2 hours with the laboratory scale measuring system  300 ′ as this is sufficient for pre-screening the given inhibitor. In the present case the measurement was only performed for a period of 5250 sec because by this time even the second differential pressure gauge  130   b  reached its upper measuring limit permanently. 
     The pressure differences measured by the differential pressure gauges  130   a ,  130   b  are plotted against time in  FIG. 5 a   . As can be seen the differential pressure gauges  130   a  and  130   b  measured about 0 bar value during approx. 2500 sec, from whereon the measured values fluctuated strongly, meaning that the gas hydrate deposited on the inner wall of the measuring cell  111 ′ was washed off by the gas stream repeatedly. After 3000 sec substantial pressure difference was observed by both differential pressure gauges  130   a ,  130   b . After approx. 5000 sec both differential pressure gauges reached their upper measurement limit. From this it can be concluded that at a temperature of 4° C. after 2500 sec the supplied inhibitor is not sufficient anymore to prevent gas hydrate formation and the gas hydrate starts to deposit on the inner wall of the measuring cell  111 ′, whereby the penetrable cross-section decreases and the pressure increases. It can also be concluded from the measurement data of the differential pressure gauges  130   a ,  130   b  that the gas hydrate formation also took place inside the first third of the measuring cell  111 ′, because the first differential pressure gauge  130   a  measured substantial pressure difference as well. The sudden rise of pressure difference at approx. 5000 sec indicates the formation of a hydrate plug, the measuring cell  111 ′ becomes highly impenetrable whereby the pressure difference drastically increases between the two sides of the hydrate plug. 
     The temperatures measured by the thermometers  140   a ,  140   b ,  140   c  are plotted against time in  FIG. 5 b   . The first thermometer  140   a  measures the temperature at the inlet of the measuring cell  111 ′ where the cooling liquid that is circulated in the heat exchange space  114  has not yet cooled the gas, thus this temperature is substantially higher. The second thermometer  140   b  is arranged at the third of the measuring cell  111 ′, while the third thermometer  140   c  is arranged in the vicinity of the outlet. The third thermometer  140   c  should measure approximately the same but always somewhat lower temperature than the second thermometer  140   b , however, as can be seen, after about 2000 sec the temperature measured by the third thermometer  140   c  starts to fluctuate, then rises after 3000 sec and surpasses the temperature measured by the second thermometer  140   b . From this it can be concluded as well that after 3000 sec substantial hydrate formation occurs within the measuring cell  111 ′. It is further noted that in contrast to the arrangement of  FIG. 4 , in the real experiment the second thermometer  140   b  was arranged somewhat upstream of the second measuring point of the first differential pressure gauge  130   a , thus it is presumed that the pressure difference indicated by the first differential pressure gauge  130   a  was caused by hydrate formation downstream of the second thermometer  140   b.    
       FIG. 5 c    shows the volume flow rate measured by the flowmeter  204  and is plotted against time. The measurement data delivered by the flowmeter  204  also allows for deducting whether or not hydrate formation occurred because, due to the hydrate deposition, the volume flow rate of the gas temporarily decreases, then it is compensated, whereby the measured volume flow rate fluctuates in accordance with the pressure difference fluctuation after 3000 sec as can be seen in  FIG. 5   c.    
       FIG. 6  illustrates a preferred embodiment of an inhibitor feeder  290  for carrying out the process according to the invention. The inhibitor feeder  290  provided for the process according to the invention comprises a telemetric data transmission system  400  (see  FIG. 7 ) for remotely controlling and monitoring the inhibitor feeder  290 . The inhibitor feeder  290  is connected to the gas well, preferably its well-head assembly  270  through a supply line  510  and is further connected through a feeding line  520  to a feeding point  310  of the gas pipeline  280  connected to the well-head assembly  270 . 
     The telemetric data transmission system  400  comprises hardware and software components, which allow for transmitting measurement data of measuring devices of the telemetric data transmission system  400  to a remote center through an electronic communication channel. 
     Electronic communication channel may be established for example within the framework of an electronic communication network, which can be a wired and/or wireless local area IT network (LAN) or a global IT network, in particular the Internet, furthermore a mobile telecommunication network employing e.g. 3G or 4G communication protocols, GSM network, satellite communication network, etc. 
     The remote center may be a dispatcher center or a server comprising programs, which when executed automatically monitor and control the inhibitor feeder  290 . 
     According to a preferred embodiment the telemetric data transmission system  400  comprises an energy supply system  320  for providing the current supply necessary for its operation. The energy supply system  320  may be a current generator, fuel cell or e.g. accumulator. According to a particularly preferred embodiment the energy supply system  320  comprises one or more solar cells  321  arranged on top of and/or beside the inhibitor feeder  290 . In case of appropriate weather conditions the telemetric data transmission system  400  may be supplied with energy for its operation directly by the solar cells  321 , or, as the case may be, the electric energy generated by the solar cells  321  may be used for charging accumulators of the energy supply system  320 . 
     The inhibitor feeder  290  preferably comprises a tank  301  for storing the inhibitor, and comprises a pump  302  connected therewith through the feeding line  520  for delivering the inhibitor into the gas pipeline  280  from the tank  301 . The inhibitor feeder  290  can be used to feed an inhibitor concentrate or, as the case may be, an inhibitor formed as the mixture of an inhibitor concentrate and an appropriate solvent (e.g. natural gas condensate, methanol). 
     According to a preferred embodiment the pump  302  is a pneumatic pump comprising a piston which is actuated by the gas supplied from the gas well through the supply line  510 , and a remote-controlled stroke rate regulator  304  regulating the stroke count per minute of the piston. The pneumatic pump  302  is preferably provided with an exhaust vent  303 . Other embodiments are also conceivable, wherein the pump  302  is not actuated by the gas pressure but instead by an electric motor. In such a case the energy supply of the electric motor is preferably ensured by the energy supply system  320  and/or the solar cells  321 . 
     In case of the pneumatic pump  302  the feed rate of the inhibitor can be set by regulating the stroke count per minute of the piston and/or the stroke length of the piston. According to a particularly advantageous embodiment the pneumatic pump  302  comprises a remote-controlled stroke length regulator  306  for regulating the stroke length of the piston. 
     The energy required for the operation of the pneumatic pump  302  is preferably ensured by the pressure of the gas coming from the gas well. The supply line  510  of the inhibitor feeder  290  is preferably connected to the well head, preferably to an upper sample outlet  274  of a conduit branch  272  mounted on the well-head assembly (Christmas-tree)  270  in order to obtain preferably dry, liquid-phase free gas from the highest point of the conduit branch  272 . 
     According to a preferred embodiment a separator  308  is connected to the supply line  510  upstream of the pump  302  for separating the liquid phase and, as the case may be, solid contaminants from the gas obtained from the gas well before the gas is introduced into the pneumatic pump  302 , whereby the lifetime of the pump  302  can be increased and the risk of breakdown reduced. The separator  308  may be substantially the same type as the above-disclosed separators  50 ,  50 ′, comprising a tank preferably filled with glycol through which the gas is blown through in order to dry it. The glycol bonds most of the liquid and contaminants carried by the gas, however, it is further possible to include one or more filters between the separator  308  and the pneumatic pump  302  in order to filter out any eventual contaminants that remained in the gas after having passed the separator  308 , whereby the gas can be further cleaned. The separator  308  preferably comprises a blow-off vent  309  through which the high pressure gas can be discharged from the separator  308  in case of maintenance. 
     According to a preferred embodiment the telemetric data transmission system  400  of the inhibitor feeder  290  comprises one or more measuring devices, for example a pressure gauge  401  connected to the supply line  510 , a liquid-level meter  402  arranged within the tank  301  and optionally a thermometer  403 , as well as a flowmeter  404  and a pressure gauge  405  the latter two being connected to the feeding line  520  connecting the inhibitor feeder  290  with the feeding point  310 , or these can form part of the assembly installed at the feeding point  310 . The telemetric data transmission system  400  further comprises one or more ground thermometers  406  (soil thermometers), which are arranged along the gas pipeline  280 . One or more physical parameters of the inhibitor feeder  290  and the environment is measured with the help of the measuring devices, such parameters may be the quantity of the inhibitor within the tank  301  and/or the temperature of the inhibitor within the tank  301  and/or the pressure at the feeding point  310 , and/or the pressure of the gas actuating the pneumatic pump  302  and/or the amount of inhibitor flowing through the feeding point  310  and/or the temperature of the environment surrounding the gas pipeline  280 . 
     The ground thermometers  406  are preferably installed below the ground level, in the vicinity of the gas pipeline  280 , whereby the local temperature of the transported gas can be estimated with good approximation. The ground thermometers  406  are preferably installed along the gas pipeline  280  upstream and downstream of the feeding point  310  at regular equal intervals or, as the case may be, at other given distances from each other. 
     According to a preferred embodiment the telemetric data transmission system  400  comprises a control unit  412  for collecting and storing the measurement data provided by the measuring devices of the telemetric data transmission system  400  and for controlling the pneumatic pump  302 . 
     The control unit  412  may be a computer, microcontroller or any other hardware device, which is suitable for storing and preferably for processing the data measured by the telemetric data transmission system  400 . The control unit  412  preferably comprises one or more input devices (for example a keyboard—not shown), one or more output devices (for example a display—not shown), and may also comprise an interface serving both as input and output device (for example a touchscreen—not shown). Preferably a communication module  414  is connected to the control unit  412  with which the measurement data may be transmitted to a remote center, e.g. a server, over a wired or wireless electronic communication channel. According to a preferred embodiment the communication module  414  may comprise a parabolic antenna suitable for satellite data transmission and the measurement data is transmitted to the remote center over a satellite communication channel. This embodiment can be particularly advantageous in such cases for example when the inhibitor feeder  290  is installed at a site (e.g. desert), where there is no conventional wired or wireless communication network. 
     The control unit  412  is in wired or wireless connection with the stroke rate regulator  304  and the stroke length regulator  306  of the pneumatic pump  302 . The wired communication may apply RS485 standard, wireless connection can be ensured for example by applying Bluetooth or ZigBee protocols as is known to a person of ordinary skill in the art. The control unit  412  preferably stores the data received from the measuring devices. 
     The inhibitor feeder  290  is connected to the well-head assembly  270  and to the gas pipeline  280  by regulators  500   a ,  500   b  and  500   c . In the context of the present invention the regulator  500   a ,  500   b ,  500   c  means a device which is suitable for regulating flow inside a pipe. The regulator  500   a ,  500   b ,  500   c ,  500   d  may be e.g. a valve, a tap or a gate valve. Regulators  500   e ,  500   f ,  500   g  may also be provided between the components of the inhibitor feeder  290  for regulating the flow. 
     According to a particularly preferred embodiment the inhibitor feeder  290  (with the exception of certain measuring devices) may be arranged inside a metal container  316  having solid walls and lockable door. The container  316  has for function to protect the inhibitor feeder  290  installed at the gas well from environmental conditions (e.g. weather), and to prevent unauthorized persons from accessing the inhibitor feeder  290 . Preferably, a motion detection sensor (e.g. reed relay, Hall-sensor, etc.) connected to the control unit  412  is arranged at the door of the container  316 , with the help of which the opening and closing of the door can be monitored from the remote center. According to a preferred embodiment the container  316  comprises a lightning guard  317  made of an electrically conducting, mechanically strong material, for example of steel. One end of the lightning guard  317  is arranged on the top of the container  316 , while the other end is buried in the ground as is known to a person of ordinary skill in the art. 
     In the following, the use of the inhibitor feeder  290  will be explained. 
     The inhibitor is fed into the gas pipeline  280  through the feeding point  310  by the inhibitor feeder  290  equipped with the telemetric data transmission system  400  at a rate determined with the help of the measuring system  100 . 
     In a first step of the inhibitor feeding process gas is extracted from the well-head assembly  270 , from which the liquid phase (practically the stratum water and the natural gas condensate) as well as the solid contaminants are separated with the help of the separator  308 . The cleaned dry gas is then introduced from the separator  308  into the pneumatic pump  302  through the supply line  510 . According to a preferred embodiment the pressure of the gas supplied to the pneumatic pump  302  is regulated with the help of the pressure regulator  401 ′. In a given case it is also conceivable to equip the supply line  510  with a regulating valve (not shown), for example a ball valve with which the supply line  510  can be closed-off. 
     The quantity of the gas reaching the piston of the pneumatic pump  302  is set with the help of the stroke rate regulator  304 . The stroke rate regulator  304  functions as a valve, which permits the flow of a given quantity of gas at given time intervals. The piston of the pneumatic pump  302  is driven by the dry gas, which is allowed to flow through the stroke rate regulator  304 . The gas driving the pneumatic pump  302  exits through the exhaust vent  303 . The inlet of the pneumatic pump  302  is connected to the inhibitor tank  301  through the feeding line  520 , and its outlet is connected to the feeding point  310  through the feeding line  520 . According to a particularly preferred embodiment the stroke rate regulator  304  is connected to the control unit  412  through wired or wireless connection. The stroke rate regulator  304  is controlled from the remote center through the control unit  412  with the help of the telemetric data transmission system  400 . Data is received from the remote center with the help of the communication module  414 , and the received data is forwarded to the control unit  412 . The control unit  412  preferably processes the received data and carries out the controlling of the stroke rate regulator  304 . 
     The quantity of the inhibitor that is delivered by the pneumatic pump  302  depends on the one hand on the stroke count per minute of the piston, and on the other hand on its stroke length. According to a preferred embodiment the feeding rate of the inhibitor introduced into the gas pipeline  280  is set to the desired value during the remote control of the inhibitor feeder  290  by remotely controlling the stroke rate regulator  304  to set the stroke count per minute of the piston. By regulating the stroke length of the piston it is possible to set the quantity of the inhibitor that is delivered by the pneumatic pump  302  even more accurately. Since in certain cases the inhibitor is supplied in only a few ml/min feed rate into the gas pipeline  280 , thus, according to a particularly preferred embodiment, the stroke length of the piston is also controlled from the remote center with the help of the stroke length regulator  306  in order to more accurately control the inhibitor feeding. According to this embodiment the stroke length regulator  306  is also connected to the control unit  412  and the remote control is accomplished as explained in connection with the stroke rate regulator  304 . Naturally, as the case may be, the stroke length and stroke count per minute of the piston, and thereby the quantity of the inhibitor delivered by the pump  302 , may be set manually on-site. 
     According to a preferred embodiment of the inventive process the telemetric data transmission system  400  also comprises the thermometer  403  and the liquid-level meter  402  connected to the tank  301 , which allow for measuring the inhibitor level and the temperature within the tank  301 . The measurement data of the thermometer  402  and of the liquid-level meter  402  are preferably transmitted to the control unit  412  over wired or wireless connection. 
     By remotely monitoring the inhibitor level and the temperature within the tank  301  it is possible to prevent or to rapidly eliminate breakdown due to any technical defect (such as defect of the tank  301 , leakage, stoppage, etc.), furthermore the continuous, undisturbed operation of the inhibitor feeder  290  can be ensured. If the measurement data shows that more inhibitor is released from the tank  301  than the quantity delivered by the pneumatic pump  302 , then it can be deduced that the tank  301  is leaking and maintenance workers may be sent from the remote center to the inhibitor feeder  290 . 
     According to a preferred embodiment the telemetric data transmission system  400  comprises further measuring devices, such as the pressure gauge  405  and the flowmeter  404  installed at the feeding point  310 . A pressure regulator  401 ′ may be installed between the separator  308  and the pressure gauge  401  in order to reduce the pressure of the gas transported inside the supply line  510 . The physical parameters measured by the above-indicated measuring devices are preferably also sent to the remote center. For example, based on the data sent from the pressure gauge  405  and the flowmeter  404  installed at the feeding point  310 , any leakage or stoppage of the feeding line  520 ,  520  may be observed, and by monitoring the pressure of the gas driving the pneumatic pump  302  breakdown of the pneumatic pump  302  can be observed. In case of any breakdown is observed maintenance workers may be sent from the remote center to the inhibitor feeder  290 . 
     According to a particularly preferred embodiment of the telemetric data transmission system  400  comprises one or more ground thermometers  406 , which are in wireless connection with the control unit  412  as discussed above. 
     According to a preferred embodiment of the inventive process the temperature of the gas pipeline  280  is measured at one or more locations by the one or more ground thermometers  406  and the measurement data is transmitted to the remote center by the telemetric data transmission system  400 . The feeding rate of the inhibitor is then corrected with regard to the measured temperatures. For example if the temperature of the gas pipeline  280  and thereby that of the transported gas decreases due to a substantial cooling of the environment, then the feeding rate of the inhibitor is increased in response of the received temperature data by the remote center with the help of the telemetric data transmission system  400  without the need to personally visit the inhibitor feeder  290 . 
     The invention has for advantage that the remote monitoring of the inhibitor feeder  290  and the gas pipeline  280  with the help of the telemetric data transmission system  400  allows for faster observation of any breakdown or environmental change, and consequently for faster reaction. A further advantage of the invention is that the inhibitor feeder  290  can be controlled remotely, thus the feeding rate of the inhibitor can be controlled remotely in accordance with the received measurement data (e.g. temperature of the gas pipeline  280 ) without field work. 
     Various modifications to the above disclosed embodiments will be apparent to a person skilled in the art without departing from the scope of protection determined by the attached claims.