141- Application of feather leaf separation and multi-factor swirl parent-child separation technologies and equipment in acetylene production and purification for PVC projects

In projects such as PVC, vinylon, PMMA, BDO, as well as all types of alkyne alcohol vitamins and pharmaceutical intermediates, there is, without exception, the troublesome issue of designing appropriate processes for acetylene production and purification. Otherwise, the first risk encountered will be the safe operation of personnel and equipment ； At the same time, the stable, efficient, and long-term smooth operation of the production line, along with issues related to its operation and maintenance costs, also arise, which are relevant to the overall efficiency of the project. This is also why peers turn to our NOVEL Technology Company for advice regarding the separation problems they encounter in their acetylene production and purification processes. I am here to discuss with everyone these common technical issues in such industries.

As is well known, the industrial production of acetylene in various projects within China’s chemical industry currently relies on two main approaches: the wet acetylene method and the dry acetylene method. The wet acetylene process is a traditional and outdated technology, but it still accounts for a significant share in the industry; heat transfer is primarily achieved through a fluidized water immersion reaction method. The dry acetylene route is an innovative approach that has emerged in recent years. Although it does not account for a large proportion of the existing industrial installations, its advantages in terms of operational safety and environmental protection, owing to its heat transfer mechanism based on water mist coverage, mean that it will become the mainstream approach.

This post was last edited by luoli519 on 2020-3-12 at 12:11. Whether it is the dry-process acetylene route or the wet-process acetylene route, the technical processes for acetylene production and purification include steps such as acetylene generation, dust and sludge removal, cooling, preliminary storage, compression, purification, neutralization, and storage. Here, we mainly discuss the separation technologies for which clients request technical support from us; this is our strength as a company named NOVEL. In the acetylene generation stage, acetylene along with water vapor, along with liquid droplets, sludge, and dust, is conveyed to the downstream pipeline equipment through the air outlet pipe located in the top space of the generator. At this stage, it is necessary to carry out the first separation and purification of the heavy-phase substances carried by the gas flow, in order to prevent such substances as liquid droplets, sludge, dust, etc. from accumulating and causing blockages in the subsequent gas transmission pipelines and equipment. This prevents disruptions in the smooth operation of the production line as well as reduces the costs associated with the maintenance of those equipment. In traditional separation process equipment, simple screen internals are often used, and the mud, dust, and alkali carried by the airflow tend to accumulate on these screens, causing blockages and leading to poor exhaust flow and pressure buildup; as a result, replacement and maintenance are required frequently. Some plant operators, due to the heavy workload associated with screen replacement and maintenance, simply remove the screen components, allowing liquid droplets, sludge, dust, and other heavy-phase substances carried by the airflow to flow unimpeded into subsequent pipeline equipment. This results in accumulation and blockages within those pipelines, as well as operational failures.

In the dust removal process, it is often necessary to remove the dust carried by the airflow. For the dry-acetylene process, since calcium carbide needs to be ground into fine particles of about 3 mm using ultra-fine grinding equipment, the processes related to grinding, screening, transportation, and reaction generate more dust as well as require more efforts for dust treatment compared to the wet-acetylene process. As is well known, dust, especially dry dust, can easily become charged and explode, which is particularly dangerous in the case of calcium carbide dust. For ultra-fine dust, the use of conventional screens, filter elements, and filter bags for interception results in a continuous increase in pressure drop during gas flow; this leads to a short service life of the filtering components and high costs associated with equipment operation and maintenance. In this stage, it is recommended to use the scrubber tower employed in the wet acetylene process, also known as a sludge scrubber tower. First, a water curtain is used to moisten and remove the majority of particulate matter and sludge of various sizes present in the gas stream. Subsequently, the liquid droplets and foam carried in the gas phase at the top of the tower, along with the calcium salts dissolved in them, are further separated. Its operational safety, efficiency, separation effectiveness, and maintenance costs make it a more attractive option. In gasification units, to effectively remove fine dust at the micron level and below present in the gas, gas scrubbers that operate efficiently, smoothly, and with low operational and maintenance costs are often chosen, offering practical advantages over dry dust removal methods.

This post was last edited by luoli519 on 2020-3-12 at 14:54. In the compression stage, it is often necessary to install a dedicated inlet separator in the compressor inlet pipeline. Some people may ask whether it is possible to reuse the inlet filter tank, since compressor manufacturers already include one such tank when supplying compressor equipment Yes, some owners specifically request the compressor equipment manufacturers to install an inlet filter tank when signing contracts for the supply of such equipment. However, compressor equipment manufacturers that install inlet filter tanks often rely on experience to determine the size of the tank and simply fit in the filter elements without giving any consideration to technical details such as the material of the filter elements, the filtering precision, or air flow distribution. As a result, issues such as high operating pressure drops, short service life, and high costs associated with filter element replacement and maintenance arise. After all, they are compressor manufacturers rather than specialized companies in separation and filtration technology, so this is understandable.

Furthermore, filter elements are effective at trapping solid particles with a constant equivalent size carried by the airflow, but they are less effective at separating droplets, mist, and sludge – substances whose equivalent size decreases as they pass through the internal components of the filter. As is known, the outlet pipe of an acetylene gas tank must pass through a water seal. Due to factors such as fluctuations in system pressure, water often ends up in the pipeline leading out of the gas tank. It is necessary to use a specialized gas-liquid separator installed on the compressor inlet pipeline to effectively remove the liquid droplets and mist carried by the gas before it enters the compressor, thereby preventing liquid slugging. However, filter tanks are not effective at removing such liquid droplets and mist, and they can easily become clogged by calcium and alkali deposits that form within them.

In the purification process, different processes for acetylene result in differences here. For the wet acetylene process, the purification step typically involves two towers arranged in series, using sodium hypochlorite solution for two-stage spray washing, primarily to convert impurity gases such as sulfides and phosphides present in acetylene gas. Due to the counter-current contact between the sodium hypochlorite solution and acetylene gas in the cleaning tower, and in order to ensure sufficient spraying intensity for the reaction and conversion of impure gases, many droplets and mist particles of sodium hypochlorite are carried by the upward airflow to the gas-phase outlet at the top of the cleaning tower. It is therefore necessary to use an efficient gas-liquid separation demister that can resist clogging caused by sodium salt crystallization, in order to remove the chlorine- and sodium-containing droplets and mist particles carried by the airflow. The screen defoamers used in traditional processes not only have low separation efficiency, but also allow liquid droplets and foam carried by the airflow to escape easily; this results in significant accumulation of liquid in the downstream pipelines as well as accelerated corrosion ； Furthermore, sodium salts tend to crystallize and deposit on the screen internals, blocking the airflow channels; this leads to a rapid increase in operating pressure drop, requiring frequent replacement and maintenance, which involves a lot of work and results in high operational and maintenance costs.

For the purification step in the dry acetylene process, concentrated sulfuric acid is often used to convert and remove impurity gases from the acetylene stream. During the purification of acetylene with concentrated sulfuric acid, the sulfuric acid gradually transforms into a dark red, highly viscous liquid that contains impurities such as high-carbon hydrocarbons and phosphoric acid. Similar to the wet acetylene purification process, the acetylene gas stream also carries and disperses sulfuric acid droplets and foam to the acetylene gas outlet at the top of the equipment. It is therefore necessary to use an anti-clogging, high-efficiency gas-liquid separator to separate and remove the sulfuric acid as well as other impurities carried by the acetylene gas stream, thereby preventing these heavy-phase substances from entering downstream pipeline equipment and causing corrosion, as well as avoiding high costs associated with subsequent treatment. Traditional mesh demisters have low separation efficiency; moreover, highly viscous sulfuric acid and impurities such as high-carbon hydrocarbons accumulate rapidly within the mesh components, blocking the airflow channels. This leads to a sharp increase in operating pressure drop, further deteriorating the separation process. It is necessary to frequently replace and maintain these components, which results in a heavy workload and harsh working conditions, posing significant challenges for the operators of such devices.

In the acetylene gas neutralization stage, the acetylene gas stream that has undergone purification enters the neutralization tower, where it reacts with an alkaline solution sprayed at sufficient intensity in a counter-current manner to effect neutralization. The acidic components present in the acetylene gas are neutralized and washed away by the alkaline solution in the spray; only acetylene gas that meets the specified standards can be sent for storage downstream or directly to the devices that use it. Inside the neutralization tower, as the acetylene gas flow moves upward from the bottom of the tower, the alkaline solution sprayed downward and the salts generated by the neutralization reaction are carried by the acetylene gas flow to the gas outlet area at the top of the tower. At this point, an efficient gas-liquid separator capable of resisting crystallization-induced clogging is required to remove the saline and alkaline droplets and mist carried in the acetylene stream, thereby preventing the accumulation of saline liquid that could cause \"fluid resistance\" and corrosion in subsequent pipeline equipment.

At each separation stage in the aforementioned acetylene production and purification processes, anti-clogging, high-efficiency separation technology and equipment are required to effectively remove the heavy-phase contaminants carried by the acetylene stream, thereby ensuring the long-term, stable, and low-cost operation of the production line and enabling the project to achieve relatively satisfactory technical, economic, and environmental benefits. The screen defoamers or filters commonly used in traditional processing technologies rely on the physical \"cells\" formed by the interconnection of screen fibers to intercept and separate the heavy-phase substances carried by the airflow, based on this separation mechanism. Due to the varying sizes of the physical \"pores\" formed by the bridging of screen fibers, some of the smaller pores trap certain heavy-phase substances, while larger pores allow those heavy-phase substances with sizes equal to those of the smaller pores to pass through and escape. Therefore, internationally, the separation efficiency of internal components such as screens is considered to be a “qualitative” separation rather than a “quantitative” one. When the airflow contains highly viscous droplets, foam, and solid particles, these heavy-phase substances get trapped on the surface of the mesh, accumulating over time and blocking the air flow channels in the mesh components. This leads to an increasing operating pressure drop in those components as well as a decline in their processing capacity; it is therefore necessary to replace and maintain these components promptly, which results in greater maintenance efforts and higher operational costs. When the airflow carries liquid droplets and foam, as these pass through the \"cells\" of the wire mesh element, their shape changes to a spindle shape, and their equivalent size also changes. When the deformed droplets and bubbles pass through the mesh pores, they return to an elliptical droplet shape under the effect of surface tension. Therefore, for droplets and bubbles in which the equivalent size of the heavy-phase carrier changes as it passes through the separation medium, techniques and internal equipment designed for filtering solid particulates, where such equivalent size remains unchanged, cannot be applied directly; otherwise, they will not be effective.