Klinkenbijl, Jeanine (Shell Global Solutions International B.V) | Brok, Theo (Shell Global Solutions International B.V) | Critchfield, Jim (Shell International Exploration and Production Inc) | Valenzuela, Diego (Shell International Exploration and Production Inc) | Lee, Danmi (Shell Global Solutions International)
The development of more complex energy sources is increasing to meet the growing demand for more energy. Such gas resources may be more contaminated, more complex, more costly, and contain more CO2 and H2S. At the same time, tighter environmental and product specifications necessitate smarter gas processing. This needs to be achieved by stretching current processes and developing reliable new technologies to effectively address the challenges of managing complex gases.
One area of gas processing that is well established is Acid Aided Regeneration (AAR) technology: the use of acids to reduce the regeneration steam of amine treating units has been applied since the 1960s, and is nowadays often referred to as a Formulated amine. Or, achieve a lower specification in the treated gas, due to a lower leanness in the solvent when the regeneration heat is kept constant, and thereby reduce environmental (CO2 and/or SO2) emissions.
Shell has carried out an extensive study on the use and misuse of AAR, focusing on the actual effects in operation and comparing unit performance with results of process simulation in the presence of acids in an amine solvent.
The operational effects observed are explained and general guidelines for application discussed. Although the focus of the application is on low pressure selective design (Tail Gas Treating Units), the main effects for high pressure application are also addressed in the study. In the paper the basis for the Shells AAR technology is described: Detailed analysis of process performance (both analytical solvent analysis and actual plant performance data) in aqueous amine treating units in a wide variety of applications. This gives good and consistent insight in the qualitative and quantitative results of acid addition to amine solvents and measured contaminant removal. A theoretical discussion on the acid effects in an amine solution, focusing on the energy for regeneration of the amine, as well as the option to meet a lower contaminant specification with a constant regeneration energy requirement by the addition of an acid to the amine solution.
Detailed analysis of process performance (both analytical solvent analysis and actual plant performance data) in aqueous amine treating units in a wide variety of applications. This gives good and consistent insight in the qualitative and quantitative results of acid addition to amine solvents and measured contaminant removal.
A theoretical discussion on the acid effects in an amine solution, focusing on the energy for regeneration of the amine, as well as the option to meet a lower contaminant specification with a constant regeneration energy requirement by the addition of an acid to the amine solution.
Bras, Ed (Shell Global Solutions International B.V.) | Klinkenbijl, Jeanine (Shell Global Solutions International B.V.) | Clinton, Paul (Shell Global Solutions International B.V.) | Van der Zwet, Gerard (Shell Global Solutions International B.V.)
Growing demand for Liquefied Natural Gas (LNG) is leading to increased production of natural gas from less attractive reservoirs. These are generally contaminated with sulphur components and located in inhospitable environments such as deep offshore waters. Conventional upstream processing in such locations is either infeasible or excessively expensive, so more and more production is by full wellstream transfer, thereby reducing the upstream facilities to the bare minimum. The consequences are that the midstream facilities need to be much more complex and require very special design attention.
This paper describes how the contaminants (e.g. hydrogen sulphide, mercaptans, carbon dioxide, water, salts, organic acids) and the necessary additives (e.g. corrosion inhibitor, hydrate inhibitor) are dealt with in the upstream and midstream designs whilst complying with ever more stringent environmental requirements (e.g. sea water quality, sulphur dioxide emissions, hydrocarbon losses). It also describes how the various contaminants and additives can interact, (e.g. forming emulsions, solids) and can cause additional problems such as foaming, fouling or corrosion.
The paper concludes that a functioning and cost-effective line-up can only be achieved by using an integrated approach, in which all the processing steps such as pipelining, separation, stabilisation, treating and NGL extraction are considered together.
Conventional & Historical Developments
Given a choice of which fields to develop, companies have always chosen the easiest and hence cheapest and most profitable ones. The consequence is that historically LNG plants have been supplied from sweet reservoirs in accessible locations.
When the undesirable constituents of the LNG plants feed gas are only carbon dioxide (CO2) and traces of sulphur components, the acid gas is called sweet. If sulphur components are present in higher concentrations, specifically hydrogen sulphide (H2S), carbonyl sulfide (COS) and organic sulphur components such as mercaptans, the gas is called sour.
When the upstream gas supply to an LNG plant is sweet and comes from an easily accessible field, it is convenient and cheap to dry the gas in the upstream facilities before pipelining the gas to an LNG plant. Consequently, the receiving facilities for such uncontaminated streams are simple. This is illustrated in figure 1, which shows a typical offshore development with a sweet reservoir in shallow water.