2016年01月13日 星期三

OS3C-5:COMPARISON OF DIFFERENT TESTING TECHNIQUES FOR THE EVALUATION OF LOW DOSAGE HYDRATE INHIBITOR PERFORMANCE

发布时间:2014-07-28
Alfred HASE, Stuart CADGER, Tracy MEIKLEJOHN, Rachel SMITH
Nalco Champion, an Ecolab Company,

  Gas hydrates are crystalline solids (clathrates) composed of cages of water molecules around natural gas molecules. They resemble wet, slushy snow when first formed. Then they compact to form an “ice” plug. The formation of hydrates in a pipeline can lead to severe problems during production including shut-down and pipeline rupture.

  There are many ways to avoid this scenario, such as operating the system outside the hydrate region, injecting the right concentration thermodynamic hydrate inhibitors e.g. mono ethylene glycol (MEG) or Methanol. An alternative chemical treatment is the use of low dosage hydrate inhibitors, which are sub divided into anti agglomerants and kinetic hydrate inhibitors.

  The pressure / temperature region the system must operate and how much thermodynamic inhibitor should be injected to prevent hydrate formation can be calculated by using modelling software, like PVT-Sim, MultiFlash or HydraFlash for instance. Selecting the right low dosage hydrate inhibitor and dose rate cannot be modelled, in order to recommend the best product for a specific application, laboratory tests are mandatory. This raises the question, which laboratory test method is the “best” one, which one provides the most reliable results?

  This paper will describe / compare three different tests methods which have been used to recommend a suitable kinetic hydrate inhibitor for a specific application. The first one was the CGI (Crystal Growth Inhibition) method developed by Heriot Watt University which determined some of the crystal growth regions that have been identified for kinetic hydrate inhibitors. As the CGI method did not provide accurate information about the length of protection against hydrate formation, additional shut in simulation tests, so called induction time tests were conducted. All these tests were conducted in high pressure stirred autoclaves.

  A third method will be describe, which allows a pre-screening of different chemistry in a short period of time, in order to create a form of performance ranking database, but will this ranking provide the best chemical to prevent hydrate formation?