146- The primary wire mesh separator at the hydrogen production inlet of the PSA pressure swing adsorption unit for coking plant exhaust gases was upgraded by replacing it with Novenergy’s vane-type separation elements

The exhaust gases from coking units, whether they are delayed coking or metallurgical coking units, contain large amounts of hydrogen and low-carbon gases, as well as small quantities of acidic gases such as hydrogen sulfide and dust. The hydrogen contained in coking off-gases is often separated to produce hydrogen using PSA, namely pressure swing adsorption technology; the pure hydrogen thus obtained is sent to hydrogenation units for use. Before entering the PSA pressure swing adsorption unit, the coking off-gases need to undergo primary desulfurization using a wet desulfurization device.

After being purified in a wet desulfurization tower, the sulfur content in coke oven exhaust gases can usually be kept at the ppm level; further treatment using a dry desulfurization tower is required to reduce the remaining sulfur to below 0.1 ppm. This is necessary to ensure that the adsorbents in the PSA pressure swing adsorption unit, especially the palladium-containing deep deoxygenation catalysts, remain free from poisoning and thus maintain their high activity and long service life. In fact, in many PSA hydrogen production processes, dry desulfurization towers have been incorporated into the PSA system as protective devices for the PSA pressure swing adsorption towers. The dry desulfurization tower not only undertakes the task of deeply removing residual sulfur from the incoming gas, but also plays a crucial role in separating and removing light hydrocarbons, as well as water vapor and liquid droplets from the gas stream coming from the wet desulfurization tower.

As is well known, dry desulfurization towers for coking off-gases are filled with desulfurization adsorbents amounting to dozens or even hundreds of cubic meters. These adsorbents not only have a saturation limit for absorbing sulfur-containing gases; light hydrocarbons and water vapor present in the incoming gas also occupy the adsorption surface of these adsorbents, thereby reducing their maximum capacity to absorb sulfur-containing gases. The desulfurization liquid and light hydrocarbon droplets/mist carried in the gas coming from the wet desulfurization tower must be efficiently separated from these droplets and mist under varying operating conditions, and this is achieved through a gas-liquid separator installed in the inlet pipeline of the dry desulfurization tower. Otherwise, the large amount of gas flow carrying desulfurization liquid and light hydrocarbon droplets enters the dry desulfurization tower and accumulates there. This not only quickly saturates the desulfurization agent used in this process but also leads to the formation of liquid pockets within the tower. As a result, it becomes difficult for the dry desulfurization tower to reach the temperature required for efficient desulfurization, and the liquid accumulation reduces the strength and lifespan of the desulfurization adsorbent. The regeneration of desulfurization adsorbents after immersion or rapid saturation requires the use of two towers that operate alternately, one in use and the other as a backup, for regeneration purposes. This process involves high energy consumption, as well as significant operational and maintenance costs and workload, posing challenges to the stable operation of the facility.

In previous PSA pressure swing adsorption units, conventional and simple mesh separators were often used as pre-gas-liquid separators in the dry desulfurization tower. The main reasons are as follows: first, the upgrading and renewal of technical equipment are not timely; second, some owners and designers do not pay enough attention to the separation equipment required at this stage of the process and are unaware of the applications of new dynamic separation technologies; third, the feasibility study report for the project as well as the investment budget were too low, which forced the use of traditional, simple screen separators. It was only when obvious problems arose during operation and affected the normal economic efficiency of the facility that technical upgrades were carried out.

Here, an in-depth discussion is provided using as an example the upgrade and modification design of the mesh separator V-02301 in the inlet pipeline of the PSA hydrogen production unit for coking off-gases at a certain enterprise, which employs the vane separation patented technology from NOVEL Company for its internal components.

The actual operating parameters of this separator are as follows: 1. Flow rate of coking off-gases: 31,700 m^3/h； 2. Operating temperature: 50℃ ； 3. Operating pressure: 0.85 MPaG ； 4. Vapor density: 0.4 kg/m^3; 5. Vapor viscosity: 0.025 cp ； 6. Special notes: The intake airflow carries desulfurization liquid mainly composed of water, light hydrocarbon droplets, dust particles, as well as foam.

This separator, V-02301, is a conventional screen separator. The problems it presents are as follows: 1. The separation efficiency is unstable, and there is significant liquid in the exhaust gas, which results in the regeneration cycle of the dry desulfurization tower being reduced from once every 2 weeks to as little as once every 3–4 days. Additionally, the service life of the desulfurizing agent decreases from 6 months to around 2 months； 2. The operating pressure drop increases rapidly; the screen internals need to be maintained and replaced every quarter or so ； 3. Maintenance workload is heavy, and operating costs are high.

Please discuss the separation in conjunction with the structural dimension drawings of this separator:

As can be seen from the figure above, the inner diameter of this screen separator is 2000 mm, while the inner diameter of the outlet pipe is less than 350 mm. Moreover, the vertical distance between the upper surface of the screen element and the airflow outlet pipe is only 537 mm. Through precise dynamic calculations using NOVEL and diagnostics conducted on the configuration design system platform, it was found that the wire mesh internals installed in the cross-section of the separator with an inner diameter of 2000 mm were, due to the contraction effect of the outlet airflow, caused to be in a non-normal or even non-functional state to a significant extent; there were substantial differences in the kinetic energy, momentum, as well as the flow pattern and regime of the airflow as it passed through these wire mesh internals. This is one of the main reasons for the abnormal operation of this screen separator.