TOTAL PRESSURE AND TOTAL TEMPERATURE MEASUREMENT IN WET GAS CONDITION |
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申请号 | EP13805398.8 | 申请日 | 2013-12-16 | 公开(公告)号 | EP2936101B1 | 公开(公告)日 | 2017-02-22 |
申请人 | Nuovo Pignone S.r.l.; | 发明人 | GERBI, Filippo; MARRAZZO, Marco; MARASCHIELLO, Francesco; MANFRIDA, Giampaolo; | ||||
摘要 | |||||||
权利要求 | |||||||
说明书全文 | Embodiments of the subject matter disclosed herein generally relate to improvements in wet gas compressor and in particular relates to probes to measure the total temperature and pressure of a hot gas mixed with liquid inside the casing of a compressor. Centrifugal compressors utilized in the extraction of natural gas often must operate in wet gas conditions since the extracted fluid contains a mixture of liquid and gaseous phases. The performances of a centrifugal compressor are modified by the presence in the gas of a liquid phase in the form of liquid droplets dispersed in the main gas flow. Many experiments have been performed on centrifugal compressor under condition of controlled gas humidity and the results show that the performances change with an increased level of the quantity of liquid contained in the gas stream. Therefore normally the liquid components are separated from the gas stream before they enter the compressor. These separator devices require a considerable amount of space and all the separation process is very expensive especially in the case of subsea operations. For this reasons the development of compressors that can operate directly with wet gas without the need of heavy, large and expensive separators is economically very attractive. In the development phase of such type of compressors, the measurements of the main thermodynamic parameters such as flow rate, fluid velocity, total pressure and total temperatures of the gas become very important for the evaluation of their performances. Unfortunately the presence of liquid droplets in the main flow that can reach a percentage in volume of 5%, depending on the gas and liquid topology causes errors in the measurement of some thermodynamic parameters, in particular pressure and temperature, when using conventional instruments, or doesn't allow the measurement at all. This is due to the fact that liquid droplets may deposit on the probe sensitive element giving rise to errors in the measurement. The entrance of the probe may also become clogged due to accumulation of the liquid droplets. Other errors rise from the aerodynamics interaction between droplets and gas with an exchange of quantity of motion that alters the measurement of the real gas pressure. Thus the measurements of thermodynamic parameters in wet gas conditions, in particular inside the casing of a centrifugal compressor, is not an easy task. For what concerns the measurement of temperature the impact of the droplets on the surface of the probe and possible evaporation, drawing heat from the probe surface, results in a temperature reading lower than the true gas temperature. Attempts to measure the pressure and temperature of a wet gas stream relies on methods to prevent the flooding by the liquid of the internal compartment of the probe or to avoid the plugging of the entrance orifice of the probe. The flooding of the probe can be partially resolved by using output orifices. For the plugging the solution found relies on the geometries and on the material employed for the orifice of the probe that can be made using hydrophilic material. In this last solution there is the necessity to substitute the hydrophilic material once is saturated with water. Other solutions foresee probes, in particular of the Pitot type, with particular complicated geometries or rely on the implementation of active systems like the heating of the input orifice to accelerate the droplets evaporation. In any case these or other more complicated solutions are not applicable for use in a centrifugal compressor or work anyway only for a low percentage in mass of the liquid phase. Besides no probe has been found that can be miniaturized to be used for measurements inside a compressor. Therefore, there is a general need to realize probes that can measure accurately total pressure or total temperature in wet gas condition also at high percentage value of liquid mass in a gas stream. More specifically, there is a need to realize miniaturized probes able to measure total pressure or total temperature in a centrifugal compressor working in wet gas regime. Therefore, a first aspect of the present invention is a probe according to claim 1. According to embodiments thereof, a probe for the measurement of the total pressure or the total temperature of a two phase wet gas flow comprises a stem, a tip on the top of the stem, a cup serving as a shield formed in the tip, the cup having a longitudinal axis generally perpendicular to the longitudinal axis of the stem and having an open front end perpendicular to its longitudinal axis by the side of the incoming wet gas flow and a closed back end on the opposite side, at least one tube or one thermal element positioned within the cup serving as pressure or temperature measuring device for the incoming wet gas flow, at least one hole which passes through the walls of the cup, and means to accelerate the wet gas flowing around the cup whereby a pressure depression is created near said at least one hole to suck the liquid, that form a phase of the wet gas flow, from inside the cup. A second aspect of the present invention is a method to measure total pressure and temperature of a two phase wet gas flow. According to embodiments thereof, a method to measure total pressure or temperature of a two phases wet gas flow comprises:
Advantageously the means to create the pressure drop around the probe consist in at least one nozzle having a longitudinal axis parallel to the longitudinal axis of the cup. A third aspect of the present invention is a system for measuring the performances of a centrifugal wet gas compressor. According to embodiments thereof, a system for measuring the performances of a centrifugal wet gas compressor comprises miniaturized probes placed inside the compressor for measuring the total pressure and total temperature of the gas stream laden with droplets of a liquid; the probes are provided with a cup wherein the gas stream can be slow down till at rest and with means to create a pressure drop around the cup in order to suck the liquid droplets from inside the cup through one or more holes formed in the walls of the cup. Further characteristics and advantages of the invention will become more apparent at the light of a detailed description of some preferred, but not exclusive, embodiments, illustrated by way of non-restrictive example, with the aid of the accompanying drawings, in which:
The following description of exemplary embodiments refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. The following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims. Reference throughout the specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrases "in one embodiment" or "in an embodiment" in various places throughout the specification is not necessarily referring to the same embodiment. Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments. |