A brief with Amen site
Sweetening sour gas with amines
Sweetening sour gas
Hydrogen disulfide (H2S), carbon dioxide (CO2), mercaptans and other impurities are commonly found in natural gas and synthetic flows. H2S is a highly toxic gaseous and causes corrosion in steel. Carbon dioxide also causes corrosion in the equipment and also lowers the gas Btu. In the process of sweetening sour gas, these impurities are removed from the gas and the gas is provided for transportation and use. The methods used for gas sweetening can be categorized in the following three ways:
Chemical
physical solution of
chemical/physical
mixes in the natural gas industry is preferred to the use of chemical solvents such as amines to other morads. But in synthetic gases, they use all methods. Common physical solvents used in this industry are methanol, dimethyl ether and propylene glycol. In the mixed state, a mixture of amino compounds and physical solvents is usually used. In general, any method that can reduce the amount of sulfur and its derivatives is preferred to other methods.
One of the old and popular methods used for sweetening is the use of amino units. Amine solvents are used in these units.
Sweetening with amines
Amine sweetening units have been used for nearly 80 years to remove H2S and CO2 from sour gas streams. Early on, the purchase of triethanolamine was used, but then mono and diethanolamine were more considered. Over the past 20 years, methyldethanolamine (MDEA) has become a popular solvent, especially because of its high selectivity in response to H2S compared to carbon dioxide.
The benefits of MDEAMEDA
have become a popular solvent in the natural gas industry due to its high selectability for H2S versus CO2. This high selectivity reduces the solvent cycle and sends a more edible H2S to the sulfur restore unit.
The reaction rate of MDEA with dihydroxide is high, while its reaction rate with carbon dioxide is much lower. The reaction rate of methyl diethanolamine with carbon dioxide is 2300 times slower than the co2 reaction rate by purchasing monoethanolamine. This solvent is very extraordinary in the removal of H2S, and is generally used to enhance the removal power of carbon dioxide, and amounts of diethanolamine (about 4%) are also used in the solvent mixture.
Stages of the sweetening process
The steps and processes taken in one of these units related to Schlumberger are as follows:
Sour gas enters the contact tower and moves upwards from the inside of the amine solvent, which flows downwards.
The refined gas comes out of the top of the tower.
The amino solution carries the absorbed acid gases with it and enters into the heat converter, called this rich solution.
The rich amine in the heat exchanger is heated by a pure amine stream that is hot.
The rich amine is also heated further in the recovery column by the heat generated by the riboiler. In this column, water and acid gases from the solvent flow are separated.
The vapor and acidic gases separated in the previous step are inserted into a condenser where they cool.
Vapor and acidic gases are also separated, the vapor flow is returned to the column and acidic gases are either burned as needed or sent to the sulfur recovery system.
The refined amine flow is also cooled first and then inserted into the initial contact tower to complete the cycle.
Various heat sources can be used for riboiler, which include direct flame, hot oil and steam systems.
In the figure below, the sour gas sweetening process is shown in full and in more detail.
Stages of sour gas sweetening process
In this process,
there are some fingertips rules that can be applied, then we will be familiar with these rules:
The temperature
difference is recommended to consider the minimum temperature difference between gas flow and pure amine flow of 5°C (10°F) when operating and designing condensers. The reason for this is to prevent the condensation of hydrocarbons in the condenser because the flow of liquid will cause problems such as foaming, reducing the life of carbon filters and reducing the product.
However, the decrease in temperature will increase the absorption of H2S, which should be considered in the design of these units.
The gas flow ratio (0.12 kg/l)
in the design of amine strippers is the flow ratio, the mass flow of vapor per volume of amines. Several sources have identified this ratio as 0.12 kg/l and have been used for many years. For the mixture flow of acidic gases, the vapor ratio will play an essential role in the quality of the final amine (leanamine) and the percentage of H2S in the final flow. The importance of this issue is greater in systems that use MDEA and need to be investigated.
The difference in the temperature of the converter
is one of the important things that many gas sweetening systems designers ignore, the difference in the temperature of the inlet and outlet streams of the converter. As mentioned earlier in this converter, two amine currents are exchanging heat, the optimum temperature difference for inlet and outlet currents is 99 °C.
The pressure
recommended that the Regenerator pressure be between 2 and 2.1 times.
The
conclusions introduced here are, as stated above, the rules of fingertip that are based on process experience and, of course, previous designs. As a rule, sour gas sweetening can experience different operating conditions in many cases, but awareness of these rules can be optimized and speed in design and operation.