STUDY OF THE DEGREE OF FOAMING OF ABSORBENT COMPOSITIONS USED WHEN PURIFYING GASES FROM ACIDIC COMPONENTS

ABSTRACT

This article presents a new MEA for purifying natural gas from acidic components - monoethanolamine; DEA – diethanolamine; MDEA – methyldiethanolamine; PEGDME – polyethylene glycol dimethyl ether; The results of a study of absorbent compositions prepared on the basis of PEGMME - polyethylene glycol monomethyl ethers are presented, and the issue of optimizing this absorbent composition when purifying natural gas from acidic components is determined. The phenomenon of foaming in gas amine drying devices is a known negative phenomenon for a long time. We know that changing the feed rate of raw materials, changing the pH and other similar technological methods to prevent the formation of foam in the absorption process will help the device to work stably. However, when the concentration of foaming agents increases in the composition of the solution, these methods become insufficient. In such cases, it is necessary to use physical, chemical, mechanical methods to reduce foam or prevent its formation.

AННОТАЦИЯ

В данной статье представлен новый МЭА для очистки природного газа от кислых компонентов - моноэтаноламина; ДЭА – диэтаноламин; МДЭА – метилдиэтаноламин; ПЭГДМЭ – диметиловый эфир полиэтиленгликоля; Приведены результаты исследования абсорбирующих композиций, приготовленных на основе ПЭГММЕ - монометиловых эфиров полиэтиленгликоля, и определен вопрос оптимизации данной абсорбирующей композиции при очистке природного газа от кислых компонентов. Явление вспенивания в устройствах осушки газов аминов является давно известным негативным явлением. Мы знаем, что изменение скорости подачи сырья, изменение pH и другие подобные технологические приемы для предотвращения образования пены в процессе абсорбции помогут устройству работать стабильно. Однако при увеличении концентрации пенообразователей в составе раствора эти методы становятся недостаточными. В таких случаях необходимо использовать физические, химические, механические методы для уменьшения пены или предотвращения ее образования.

Keywords: components, absorbents, acid components, absorbent compositions, optimization, determination procedure, mathematical models, optimality criterion, optimal limits, model coefficients.

Ключевые слова: компоненты, абсорбенты, кислотные компоненты, составы абсорбентов, оптимизация, процедура определения, математические модели, критерий оптимальности, оптимальные пределы, коэффициенты модели.

Introduction

Sour gases are highly aggressive substances. Hydrogen sulfide has an aggressive effect on steel like an acid and causes the oxidation of insoluble iron sulfur. When carbon dioxide is present in water, it reacts with metallic iron to form iron bicarbonate, which, when the solution is heated, is formed into insoluble iron bicarbonate, which is deposited on the walls of the internal surfaces of the apparatus and in pipelines. Corrosion accelerates under the influence of products of amine degradation (meeting into tanzanol), which interact with metal. Therefore, scientists in this field have conducted many scientific studies.

G.A. Agayev, A.S. Kuliyev and V.V. Research was carried out by Nemkov to determine the causes of foam formation during amine purification of natural gas from sour components [1].

Including G.A. Agayev, A.S. Kuliyev and V.V. Nemkov researches were carried out to determine the causes of foam formation in the amine purification of natural gas from sour components. Y.F. Vysheslavsev and his colleagues studied the causes of foam formation in the process of cleaning gas from sour components with DEA solution. The problem of studying the causes of foaming of solutions and the causes of foaming of aqueous solutions of DEA with organic solvents [1, 2] was raised.

M.P.Smojok and G.A.Krasovskaya created a general formula of cyclobranched structures of polyethylenesiloxane.

S.I. Mindlin and P.S. Zasipkin offers new foam extinguishers based on alkylpolysiloxane polymers, which use polyoxymethylenemethylsiloxane as polymers [3].

Y.F. Visheslavsev and his colleagues [4] studied the causes of foam formation in the process of cleaning gas from sour components with DEA solution. The problem of studying the causes of foaming of solutions and the causes of foaming of aqueous solutions of DEA of organic solvents is set.

P.R. Gaub, G.G. Kotov and V.A. The Sazonovs [5] recommended foam extinguishers made of organic silicon compounds ETS-31, ETS-40, ETS-50, KAV-1, muddy KIL, processed silicon organic liquids as foam extinguishers.

N.W. Vvedensky, L.A. Mitrofanov and A.V. Karlins proposed a foam extinguisher based on silicon organic polymer, which was obtained by oxidation condensation α, ω-polydimethylsiloxanediol with relative molecular mass (20 ÷ 40) thousand and hydroxyl group with 0.2% aluminum hydroxide.

P.R. Gaub, G.G. Kotov and V.A. Sazonov recommended as foam extinguishers ETS-31, ETS-40, ETS-50, KAV-1, clay KIL, recycled silicon organic liquids [5].

In order to solve these problems, it is necessary to know the properties of natural gas and its characteristics in production conditions, to research the procedures for the operation of new devices for the qualitative purification of the composition of natural gas from sour components and various impurities in its transportation and storage, in the use of various technological processes and energy devices, and the use of absorption methods in gas purification. the use of combined cleaning technology, research issues of developing new absorbents are considered [6, 7].

The analysis of the process of amine purification of natural gases from sour mixtures was carried out, the problems that occur together and ways to solve them were considered. Such issues, i.e. optimization of the composition of amine solution and separated sour gases, problems of pollution of amine solutions, high energy consumption in their regeneration were analyzed. Issues of foam formation in the absorber and ways to reduce it, the main directions of disposal of processed amines are considered.

The main stages of preparing natural gas for processing are the removal of sour compounds, primarily hydrogen sulfide and carbon dioxide, resulting in the formation of raw materials for the production of commodity gas and sour gases, as well as gaseous sulfur [6, 7, 8, 9].

Alkanolamines are widely used in the purification of gases from sour mixtures, in which case they have low viscosity, are effectively purified from H₂S and CO₂ in a wide range of partial pressures, and almost do not absorb hydrocarbons (UV) [7, 10, 11].

However, the technology of absorption with alkanolamines has serious disadvantages: high energy costs in the regeneration of amines, destruction of amines, contamination with various impurities, foaming during absorption, etc.

In order to increase the concentration of hydrogen sulfide in sour gases, it is necessary to choose an absorbent that is selective for H₂S, suitable for cleaning natural gases.

However, today the Mubarak gas processing plant (MGQIZ) - the main sulfur producer in Uzbekistan - uses diethanolamine (DEA) as an absorbent, which is non-selective towards H2S.

The absorbent can be replaced with tertiary amines, i.e. methyldiethanolamine (MDEA), which is selective for hydrogen sulfide and practically does not remove H₂S and CO₂. In this case, a large amount of CO₂ will remain in the composition of the commodity gas, as we have already considered the requirements for it. To increase the selectivity of H₂S, a mixture of  DEA and MDEA can be used, as we have shown in our previous works, and the permissible content of carbon dioxide in the product gas should not be exceeded, for this, the optimal content of MDEA in the mixture is selected [7, 11].

There are many reasons for the formation of foam, especially among them:

increased corrosion in devices; various substances fall into it during gas extraction; falling heavy drops of heavy UV rays on the absorber; decomposition of amines under the influence of high temperatures; accumulation of products of secondary reactions and decomposition of amines; drops of water on the gas; the presence of mineral salts in technical waters, which are used to obtain an absorbent solution [12, 13]. Foam formation leads to deterioration of gas quality, loss of absorbent, violation of device operating modes and decrease in performance indicators, pressure differences in the device (which are the main causes of foam formation).

Foaming leads to equipment failure, deterioration of the quality of purified gas, and, in return, to a decrease in the performance of the gas equipment. During foaming, the amount of loss increases as a result of the removal (volatilization) of expensive amines with gas [2, 7, 12, 13], a part of which is captured in the gas glycol drying system, the main flow of which is taken to the main gasification through the gas stream.

A large accumulation of MEA and DEA in the glycolic solution will eventually increase the freezing temperature, that is, cause hydrate formation and clogging of the heat exchange equipment during gas purification.

During foaming, energy resources are used without saving, so tens of tons of amine and glycol are required. Therefore, it is very important to develop the causes of foaming in factory conditions and methods of its prevention in gas purification.

According to the order of foaming - it also appears in absorbers. There are cases when the beginning of foaming of the solution moves to the desorber. Foaming often occurs in equipment with high gas and solution loads. The signs of foaming are an increase in the volume of foam in the contact plates, a sharp increase in the pressure difference in the devices, a large liquid level in the separators of purified (absorber) and sour (desorber) gases.

The main causes of foaming are particles, which enter together with the raw gas and fall into the absorbent (liquid hydrocarbons, formation water, mechanical particles, corrosion inhibitors, various SFM, tar substances, etc.). Iron sulfide, lubricating oils, corrosion products, and amine breakdown are also foam formers. These products are also concentrated in the solution to a certain concentration, which begins to foam it.

It can be seen from these data that in practice, all substances entering the mine with gas have the property of foaming amine solutions. The most foam formation is caused by hydrocarbons, that is, with a boiling point above 100°C (condensate, oil), SFM, some corrosion inhibitors. G.A. Artyushenko, Sh.M. Sabirov, L.I. Majalar [22, 40, 179] studied the effect of monoethanolamine aqueous solutions on the dissolution of salts, and experiments of adding MgCO₃, CaCO₃, KS1, K₂SO₄ to a 15% solution of MEA were presented. The results show that such salts, like calcium and magnesium carbonates in the amount of 0.4%, increase the foamability by 2 times, while chlorides and sulfates reduce it. The foaming of a mixture of absorbing solutions of these salts has a low speed.

The absorbent compositions obtained as a result of the research of the operational properties of the absorbent compositions used in the purification of gases from sour components, the operating conditions with amines used in gas processing plants today, their chemical changes in the conditions of their use, and the impact of these changes on their operational properties in order to learn the secret, the main properties of these absorbent compositions were studied.

The increased foaming of amine solutions (especially MEA and DEA) in the absorption purification of natural gas from acidic components is a complex problem associated with various particles formed as a result of various processes in their composition [16]. Therefore, the degree of foam formation was studied with their pure solutions and various substances in their composition, including corrosion inhibitors, hydrocarbons, mechanical particles, decomposed products of different concentrations formed in natural gas desulfurization devices.

A 30% solution of DEA, which is currently used in gas processing plants for gas purification, was also studied. A 30% solution of DEA was taken as a standard. At the same time, the effectiveness of "Qutramin 1001" foam suppressant on the degree of foaming of amine solution poisoned with various substances was also studied.

Processing of natural gas includes a device for cleaning sour components, which are capable of corroding the equipment of its processing processes and the amount of which is strictly limited in the composition of the commodity gas product. Today, according to the technological regulation, the amount of hydrogen sulfide and carbon dioxide in the content of gas that has undergone absorption purification is 0.012% and 0.02%, respectively. If the amount of these sour components in the raw gas content is up to 2-50%, in this case, liquid phase processes and physical absorbers with the participation of an aqueous solution of amines are used to clean this raw material. In the world, the processes of absorption purification of gases from acidic components using amine solutions occupy a leading place.

Currently, one of the main negative features of gas absorption purification processes using amines in the industry is the foaming phenomenon, which is formed due to various substances falling in the absorption process together with the raw gas and due to the wear of the absorbent [16]. Various substances in the gas environment include salts, mechanical particles (corrosion products, formation particles), hydrocarbons dissolved in the gas, corrosion inhibitors, substances in gas production acid treatment and well intensification, substances formed as a result of decomposition and oxidation of amines.

Analyzing the operation of the gas treatment plants from sour components in gas processing plants, the average amount of mechanical particles in the composition of amines is 0.020%, iron compounds are 0.002-0.003%, corrosion inhibitors are 0.002%, thiosulfates formed as a result of the operation of amines are 0.3 % ( (NH₄)₂S₂O₃, MeS₂O₃, Me(S₂O₃)₃, H₂S₂O₃), chlorides 1% and heat-resistant salts 450 mg/dm³. Decomposition of amines was mainly observed at high temperatures, and it was shown that their content can reach 15-18% in the composition of amine solutions. The amount of liquid hydrocarbons dissolved in gas is 3-4%. These hydrocarbons slowly pass into the amine solution, and since the desorption temperature is not sufficient to separate them, they accumulate in the solution [15].

As a result of the accumulation of various particles and substances formed as a result of the aging of the amine in the composition of the amine solution, it causes the absorbent to suddenly foam. This, in turn, causes the release of amine in the gas purified from the absorber and the poisoning of the adsorbents used in the gas drying unit. In addition, foaming leads to a deterioration of absorbent capacity and a decrease in the overall capacity of the device [15, 16].

The phenomenon of foaming in gas amine drying devices is a known negative phenomenon for a long time. Scientists from all over the world have been conducting their scientific research for a long time to solve this unpleasant phenomenon [1, 2, 10, 11, 17].

We know that changing the feed rate of raw materials, changing the pH and other similar technological methods to prevent the formation of foam in the absorption process will help the device to work stably. However, when the concentration of foaming agents increases in the composition of the solution, these methods become insufficient. In such cases, it is necessary to use physical, chemical, mechanical methods to reduce foam or prevent its formation [16, 18, 19].

30% DEA used in gas absorption cleaning processes and the foaming ability and foam stability indicators of DPP-1, MDPP-2, MDPP-5 absorbent compositions obtained as a result of scientific research in pure absorbent samples and their content 0 It was determined by adding a model mixture of liquid hydrocarbons prepared by mixing liquid hydrocarbons found in gas in concentrations of 1-1% (С₅H₁₂ – 20% + C₆H₁₄ – 20% + C₇H₁₆ – 20% + C₈H₁₈ – 20% + C₉H₂₀ – 20). The obtained results are shown in Figures 1 and 2.

The results of the study on determining the foaming of absorbent compositions pure and at different concentrations showed better results of absorbent compositions DPP-1, MDPP-1, MDPP-2 and MDPP-5 compared to DEA. This can be explained by the fact that small amounts of PEGDME and PEGMME in absorbent compositions prevent foam formation.

Figures 1. Dependence of the ability of absorbent compositions to form foam on the concentration of liquid hydrocarbons

We can see that the addition of liquid hydrocarbons at a concentration of 0.25% to the composition of the absorbents had a positive or no effect on the foaming ability of almost all absorbent samples. At higher concentrations, it had a negative effect on the ability to form foam, that is, the height of the foam increased. The results of this study show that DEA and MDPP-2 absorbents maintain a low foaming capacity at up to 0.5% liquid hydrocarbon content, while DPP-1, MDPP-1 and MDPP-5 absorbents maintain up to 0.75% liquid hydrocarbon. It was found by experiments that it retains its foaming ability in this class even in the presence of hydrocarbons.

Figures 2. Dependence of foam stability of absorbent compositions on the concentration of liquid hydrocarbons

We can see that the addition of liquid hydrocarbons at a concentration of 0.25% to the composition of the absorbents had a positive or no effect on the foaming ability of almost all absorbent samples.

 The results of the study on determining foam formation of pure and different concentrations of absorbent compositions showed better results of DPP-1, MDPP-1, MDPP-2 and MDPP-5 absorbent compositions compared to DEA. This can be explained by the fact that small amounts of PEGDME and PEGMME in absorbent compositions prevent foam formation.

The dependence of the foam stability of absorbent compositions on the concentration of liquid hydrocarbons. The results of the research show that when the concentration of liquid hydrocarbons in the absorbent composition is 0.5%, DPP-1, MDPP-1 and MDPP-5 absorbents correspond to the low foam stability class. while the foam breakdown of DPP-1 absorbent with liquid hydrocarbon concentration up to 0.75% was 56 seconds, and that of MDPP-5 absorbent was 52 seconds. DEA and MDPP-2 absorbents showed much lower foaming stability results.

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