206-For the gas extraction liquid ring pump used in coalbed methane operations, an upgraded separation system using a vane separator is adopted for the separation of the exhaust gas, xanthan gum solution, and other components

This post was last edited by luoli519 on 2022-6-1 15:03. Coalbed methane (coal mine gas) extraction is a form of industry support that combines aspects related to coal mine production safety and environmental protection, as well as those associated with new energy sources; it has already developed into an established industry. However, gas extraction technology is complex, energy consumption is high, and there are significant safety risks associated with the operation of underground gas extraction systems. The core process equipment in traditional technologies uses water ring pumps for gas extraction. Water ring vacuum pumps utilize water as the working medium and carry out gas extraction and discharge through isothermal compression; they offer safe and reliable performance, which is why they are widely used in coal mine gas extraction. However, their operational efficiency is low and their energy consumption is high.

This post was last edited by luoli519 on 2022-6-1 at 19:23. The water ring vacuum pump was first introduced to China using technology from German Siemens, and after over a hundred years of development, it has become a mature product. However, the high energy consumption and low efficiency of water ring vacuum pumps are serious problems that need to be addressed urgently, especially when used for coalbed methane extraction. Some domestic universities and research institutions have added polymer enhancers such as xanthan gum to water, the traditional working fluid, in order to reduce the operating power consumption of gas extraction pumps. This approach has helped overcome the technical limitations associated with high energy and water consumption in water ring vacuum pumps. By switching from an open-loop system to a closed-loop circulation system, significant energy savings have been achieved, resulting in considerable economic benefits. This has contributed to the upgrading of China’s water ring vacuum pump industry, improved the safety levels in coal mining operations, and brought about notable social benefits as well. The attached figure is a picture of the device for its technical application:

This post was last edited by luoli519 on 2022-6-1 at 19:27. Since high-molecular efficiency enhancers such as xanthan gum are added to the working fluid, the exhaust flow from the liquid ring pump inevitably contains a significant amount of these enhancers; it is necessary to capture and reuse them in order to reduce operating costs. The gas-liquid separator used in closed-loop systems is a traditional multi-baffle separator; in China, this low-cost and simple swirl separator has been widely used since the middle to late 20th century, and it is still manufactured and utilized, especially in the East China region. The main problem with the operation of multi-stage separators is that their low cost results in a simple structure, which in turn leads to poor separation performance; as a consequence, a large amount of the polymer efficiency enhancer xanthan gum is lost. The image below shows the picture 1 of the multi-stage separator housing used in its technical application project:

This post was last edited by luoli519 on 2022-6-1 19:28. The top view of this clutch separator housing is as follows:

The last edit to this post was made by luoli519 on 2022-10-28 at 14:14. The gas-liquid mixture pumped out by the liquid ring pump (which actually also contains some coalbed methane dust) enters the separator shown in the diagram above. To prevent air currents from entering the working fluid pipeline during liquid drainage, an inverted U-shaped liquid seal is provided on the drain pipe of the check separator shown in the diagram above. Please refer to its side view 3:

This post was last edited by luoli519 on 2022-6-1 19:42. The gas-liquid mixture inlet of the clutch separator is located in the upper middle part of the tank, entering the housing tangentially for separation. Due to the short swirling path of the fluid within the complex baffle separator, the liquid flows to the bottom of the separator under the effect of gravity and is discharged through the pipes at the bottom of the vessel, while the gas moves upward to the top of the separator tank and is expelled through the exhaust pipes at the top. An access hatch is usually provided in the middle section of the tank for maintenance purposes. The following figure is a cross-sectional view of the multi-stage separator tank:

The multi-stage separator is a type of semi-empirical separation device that is used only in China and rarely abroad. In the multi-stage separator, in addition to separation by gravity settling, the fluid also undergoes a certain degree of swirl separation. However, since the theoretical rotation distance of the gas-liquid mixed flow vortex is only 3/4 of a circle, and it is difficult for the actual vortex to achieve this distance; moreover, the radii of each set of baffles arranged in concentric circles vary, resulting in different separation effects and rotation distances due to the rotation of the fluid. As a result, the separation efficiency of each set of baffles differs, allowing them to be used only for basic separation tasks, not for precise and quantitative separation.

This post was last edited by luoli519 on 2023-3-23 at 13:53. The top view of the internal components of the clutch separator is provided here. As can be seen from the top view of the internal components of the multi-baffle separator, an air stream enters the separator tangentially and is then divided into multiple streams that flow into the concentrically arranged multi-baffle swirl vanes. The closer the vane is to the center of the circle, the smaller its rotational radius becomes; this results in a higher centrifugal factor. However, the operating pressure drop increases, the fluid’s rotational path shortens, and the degree of separation decreases ； The further a vane is from the center of the circle, the larger its rotational radius becomes; as a result, the centrifugal factor decreases, but the operating pressure drop is lower. The fluid rotates over a longer distance, leading to an increased degree of separation. Therefore, a pair of conflicting factors lead to a compromise in operation, resulting in poor separation performance.

The separation performance of the multi-stage separator is poor – how poor is it? Customers have reported that they require the amount of residual exhaust liquid after separation to be 1 g/m^3 of gas, but in actual operation the amount of residual liquid in the gas stream after separation remains at 20–30 g/m^3. This results in excessive losses of polymer efficiency enhancers, thereby leading to significantly higher operating costs.

This paper takes the actual operating conditions of the exhaust gas recirculation and separation separator equipped with a high-molecular efficiency enhancer in a coalbed methane extraction project in North China as an example for analysis and discussion. Based on the information provided by the customer regarding the exhaust gas emission process of the vacuum pump, the exhaust gas from the vacuum pump enters the existing multi-baffle separation tank, which has an ID of 1600 mm and dimensions TL/TL of 2155 mm, through an inlet pipeline with a diameter of 530 mm located at the upper part of the separation tank. Under operating conditions of a temperature of 45°C and a gauge pressure of 5 kPaG, the exhaust gas flows at a rate of 220 Nm^3/h and enters the tank tangentially. After undergoing separation via multi-baffle cyclone action and gravity sedimentation, the exhaust gas is then discharged. It comes from the exhaust gases of the vacuum pump and consists of air, methane, water vapor, etc. The exhaust gases carry a xanthan gum solution at a concentration of 1100 g/Nm^3; under the aforementioned conditions, this xanthan gum solution has a density of 996 kg/m^3 and a viscosity of 21 cp. Due to the low operating efficiency and instability of the original separator in carrying out gas-liquid separation, liquid contamination in the exhaust gas was relatively severe.