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Condensed Rotational Separation to upgrade sour gas

By JJH Bert Brouwers and HP Erik van Kemenade


A steadily increasing amount of newly located natural gas fields is severely contaminated with CO2 and/or H2S. Percentages of 30 % CO2/H2S or even larger are not uncommon. Fields with such high degrees of contaminant can not be economically exploited by conventional techniques based on amine treatment, as implementation would lead to a huge energy consumption. Moreover, capital costs involved with the erection of the installations would be very large [1]. Thus, there is a need for alternatives which do not suffer from these shortcomings. Condensed rotational separation, abbreviated as CRS [2] forms such an alternative. In addition to upstream applications, for purifying natural gas [3], the technique also has potential for removing CO2 from combustion effluent, CO2 from syngas and condensates from natural gas.CRS is a simple and straightforward method to upgrade heavily contaminated gases to light degrees of contamination of only a few percent. The size of the installation is small; the energy required to do the job is only a small fraction of the heating value of the produced methane. CRS is a cheap process which makes heavily contaminated gas fields almost as economic as lightly contaminated fields.The working principle of the patented CRS process is as follows. The sour gas is rapidly lowered in temperature (-50/-80oC) and/or reduced in pressure (20/40 bar) by applying compact coolers and expanders. A mixture forms which consists of predominantly gaseous methane with in it a mist of small micron-sized droplets consisting of predominantly liquid CO2/H2S. The liquid droplets are separated by applying the patented apparatus of the rotational particle separator, abbreviated as RPS (Figure 1). The process is further enhanced by introducing a second step of regeneration. The collected liquid is reduced in pressure (~10/20 bar). In this way most of the methane which was dissolved in the liquid evaporates. The gas has a composition roughly equal to the incoming feed gas. It is re-fed into the gas stream in the first part of the process.Essential in the process is the availability of the rotational particle separator (RPS). Although not widely known, rapid cooling of binary or multi component mixtures of gases to temperatures where one, or some of the components preferentially condense, leads to a mist of very small droplets with diameters of 1 to 10 micron. The phenomenon is known to occur by aerosol formation in flue gases of biomass combustion installations [4], condensate droplets resulting from cooling of wet natural gas [5] and fog created downstream of windmills, Figure 2. It has also been measured in experiments with Ch4/CO2 mixtures and CO2/N2 mixtures [6,7]. For a process which relies on fast phase change as a means of separation to be economical and practical, it is necessary to have a device capable of capturing micron-sized droplets with high collection efficiency, low pressure drop and small building space. The RPS is such a device In this paper we shall address the important aspects of CRS. In section 2 a description is given of the thermodynamics of the process. Section 3 deals with the rotational particle separator, while in section 4 a presentation is given of the sizing of an installation capable of handling a field of 100 MMscf/day with composition 59 %mole CH4, 27 %mole H2S and 14 %mole CO2 (this corresponds to the Huwaila field in Abu Dhabi). Other applications of the CRS technology are discussed in section 5, conclusions are presented in section 6

Year: 2010
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Provided by: Repository TU/e
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