IBP2323_08 AMINE DEGRADATION AND ASSOCIATED PROBLEMS IN THE GAS TREATING UNIT E.R.Baumeister1 , R.C.O.Souza2 Copyright 2008, Instituto Brasileiro de Petróleo, Gás e Biocombustíveis - IBP Este Trabalho Técnico foi preparado para apresentação na Rio Oil & Gas Expo and Conference 2008, realizada no período de 15 a 18 de setembro de 2008, no Rio de Janeiro. Este Trabalho Técnico foi selecionado para apresentação pelo Comitê Técnico do evento, seguindo as informações contidas na sinopse submetida pelo(s) autor(es). O conteúdo do Trabalho Técnico, como apresentado, não foi revisado pelo IBP. Os organizadores não irão traduzir ou corrigir os textos recebidos. O material conforme, apresentado, não necessariamente reflete as opiniões do Instituto Brasileiro de Petróleo, Gás e Biocombustíveis, seus Associados e Representantes. É de conhecimento e aprovação do(s) autor(es) que este Trabalho Técnico seja publicado nos Anais da Rio Oil & Gas Expo and Conference 2008. Resumo A degradação das aminas e os problemas relacionados em uma unidade de tratamento de gás, não podem ser evitados ou eliminados completamente, entretando, podem ter seus custos eficazmente atenuados usando um programa profundo de gerenciamento da unidade. Os benefícios econômicos e de desempenho, a partir de um programa de gerenciamento da amina, incluem diversas melhorias e índice de desempenho. Melhoria de desempenho, custos operativos mais baixos, e baixo impacto ambiental são algumas das vantagens adicionais de se usar um sistema de gerenciamento detalhado de uma unidade de tratamento de gás. Summary Amine degradation and associated problems in the amine gas treating unit cannot be completely avoided or eliminated. They can be cost effectively mitigated using a thorough amine management program. Economic and performance benefits realized from an amine management program include several improvements and performance index. Better yields, lower costs, and fewer environmental concerns are some of the additional advantages of using a comprehensive amine management system to help run the amine gas treating unit. Abstract Amine based gas treating systems can have problems with solvent degradation for many reasons including operating conditions that permit inlet contaminants. This degradation can lead to frequent troubleshooting of the amine system. One important consequence of degradation is the formation of Heat Stable Amine Salts (HSAS). We define HSAS as the amount of amine cation required to neutralize acids not regenerated under normal regenerator conditions. Heat stable salts in amine solutions, as amine or stronger base salts, can cause a number of operational problems. All of these problems have been experienced in numerous applications of amine treating. ______________________________ 1 Ph.D. in Organic Chemistry; Senior Technical Service Specialist – Dow Chemical Co. 2 Chemistry Bachelor; Senior Oil &Gas Development Specialist – Dow Brasil S/A Rio Oil & Gas Expo and Conference 2008 • Corrosion and erosion of metal components are accelerated by the precipitation of salts or corrosion end products. • Foaming may be caused by changes in the surface active character and the increased viscosity of the solution. • Reduced acid gas carrying capacity is the result of less amine present in a usable absorptive state. Reduction or removal of heat stable salts ultimately requires reclaiming the amine solution by electrodialysis, vacuum distillation, ion exchange resin treating, dilution through purge and make up or total solvent replacement. The challenge lies in identifying the acceptable operating limits of heat stable salts and preventing the escalation of these problems. It is apparent that a number of factors must be included in determining those limits. Heat stable amine salts are formed with acidic components other than H2S and CO2 in the inlet process stream to the amine absorber. Typical acidic components include acids that form salts of chloride, sulfate, formate, acetate, oxalate, cyanide, thiocyanide, and thiosulfate. In addition, oxygen absorbed into the amine solution creates amine oxidation products that include formate, acetate, and glycolate. Many factors must be considered when determining a reasonable limit of heat stable salts in amine solutions. These can be broadly categorized as one of the following: • The character of the heat stable salt species. • The operating conditions of the amine unit. • The mechanical design of the amine unit. The term "heat stable" is a broad term used to describe a number of undesirable salts in an amine solution. They are undesirable because they cannot be effectively removed in the normal pressure/temperature swing in the absorption and desorption cycle of gas treating within amines units. In actuality, the stability of these salts depends on the species of the anion and cation which makes up the salt. In this paper we will cover common aspects involved with amine degradation, explaining the reason they occur, the different degradation for each amine used for acid gas removal, the consequences in the system and how to control them thru an Amine Management System, based on a low total cost approach to treat HSAS, reduce contamination, and minimize corrosion. 1. Introduction Amine solvent formulations are used to remove acidic components such as CO2 and H2S from gas streams to comply with sales gas specifications for end use or to make the gas suitable for liquefaction. During operation of an amine unit, degradation of the solvent occurs due to reaction with contaminants like oxygen, sulfur dioxide, and acids or acid precursors in the feed gas. Some of the tertiary amine oxidation products include secondary amines. These degradation products lead to a number of operational problems in the amine units if allowed to build up in concentration. Build up over time is related to solvent age, use and handling and will occur in every amine solvent. Common Operational Problems include: 1. Increased corrosion rates, particularly at the lean side of the amine unit. 2. Fouling in those parts of the unit where solvent flow velocities are low and the solvent loading of H2S or CO2 is high, i.e. the trays and the bottom of the contactor and the lean/rich heat exchanger. In “CO2-only” systems, 2 Rio Oil & Gas Expo and Conference 2008 fouling tends to occur more often in the regenerator overhead. Fouling of the heat exchanger leads to a reduction in heat transfer and an increased steam use for regeneration. Ultimately, plugging of the heat exchanger may occur, restricting solvent circulation and treating capacity. 3. Decreased treating capacity of the unit due to lower amount of active amine available for acid gas removal. 4. Increased foaming tendency of the solvent from higher levels of suspended solids (also requiring a higher rate of filter change outs). 5. A high flash gas production due to a high carry-under of gas with solvent in the main absorber. 6. Decreased CO2 slip due to the presence of secondary amines. One of the oxidation products, bicine, does present problems in H2S removal applications where all of the H2S is removed from the amine solution. In the regenerator, the bicine-iron complex is decomposed in the presence of H2S. The overall result is a high activity of the “iron pump” mechanism leading to high corrosion rates and associated fouling problems. Careful monitoring of the operation of the unit in combination with measuring solvent composition and solvent properties, combined with good solvent maintenance practices will ensure reliable operation of the amine unit. 2. Amine Treatment Unit Amine treatment units are typically employed for the removal of acid components from natural gas. Depending on the concentration of CO2 and H2S in the gas, the required specification of the treated gas and the required selectivity of the removal of H2S over CO2, an appropriate alkanolamine formulation are chosen. Due to an increased environmental awareness and stricter operational disciplines, many gas-treating plants have reduced solvent losses and the subsequent make up with fresh amine. This has resulted in build up of amine degradation products becoming an important issue. A solvent quality monitoring service can be used to measure the amine composition of the solvent and to determine the presence of acid components and heavy amine degradation products. Because the amine unit uses an aqueous solution of the amine, absorption of hydrocarbons, mercaptans and organic sulfur species from gas streams is minimal. MDEA is normally chosen when a high selectivity for H2S absorption relative to CO2 is of paramount importance. Other amines used in refinery applications are DEA (di- ethanolamine), MEA (monoethanolamine), DGA (di-glycolamine), sterically hindered amines and various specialty amines which are proprietary mixtures of amines and additives to improve selectivity, kinetics and stability. 3. Amine Contaminants and Degradation 3.1. Contaminants Amine contaminants can be grouped into four distinct categories; (1) heat stable salt anions, (2) injection chemicals, (3) hydrocarbons and (4) particulates. All of these contaminants categories are typically present in any given amine system at the same time, although the amount of each one can vary from insignificant to several percent. 1) Heat Stable Salts: Acid anions such as formate, acetate, thiosulfate, thiocyanate, and chloride can tie up an amine molecule to form a salt that is not capable of being regenerated by the addition of heat, and are thus referred to as Heat Stable Salts.