Hydrogenated Reaction Feed Furnace
The Hydrogenation feed furnace is the key equipment in the device. The process medium in the furnace tube is high temperature and pressure hydrogen & oil and gas mixture, and the operating conditions are very demanding. The mixed hydrogen in Hydrogenation reaction furnace is divided into pre-furnace hydrogen mixing and post-furnace hydrogen mixing. The two hydrogen mixing methods have their own characteristics.
In a pure liquid phase furnace, the choice of flow rate is primarily concerned with reducing pressure drop and avoiding coking. The flow rate is high, the turbulent flow state can be achieved, the oil film temperature difference can be reduced, local overheating can be avoided, and the scouring action can be performed at the same time, so that the coke layer is detached quickly, which is advantageous for avoiding coking.
However, the pressure drop is proportional to the square of the flow rate. Excessive flow rate not only increases the power consumption of the pump, but also increases the pressure rating of the equipment and accessories upstream of the Furnace, increasing the investment. Conversely, when the flow rate is lowered, especially when the flow rate is low to the laminar flow state, coking is almost inevitable. In addition, when the flow path is over the two, the low flow rate is also prone to bias current.Once a bias current occurs, the coking resistance increases and a more biased current vicious cycle can quickly lead to Furnace tube burn-through. For the Furnace of Pre-furnace hydrogen mixing, in the furnace tube of the gas-liquid two phase flow, the flow pattern should be considered while selecting the flow rate.The flow pattern of the two-phase flow is generally divided into a wavy flow, a foam flow, a long bubble flow, a liquid throttling, a ring mist flow, and a mist flow.In addition to the molar ratio and physical properties of gas-liquid phase, the flow pattern mainly depends on the flow velocity. In order to avoid coking, the flow rate (mixing flow rate) should be minimal to ensure a ring mist flow and a mist flow.In order to avoid coking, the flow rate (mixing flow rate) should be minimal to ensure a ring mist flow and a mist flow.Considering that the oil in the Furnace for Pre-furnace hydrogen mixing tends to have a large coking tendency, it should be designed to achieve a ring mist flow at 70% of the treatment amount. Of course, in actual operation, if the treatment amount is lower than 70%, measures such as increasing the ratio of hydrogen to oil can be taken to ensure high flow rate.
The biggest problem of Pre furnace hydrogen mixing is the problem of gas-liquid two-phase flow distribution in the medium of the large-capacity device furnace tube. The greater the load on the device, the more prominent this problem.Therefore we need a full calculate before the design of Pre-furnace Hydrogen mixing and obtain the optimized results. The General Reaction Furnace adopts the horizontal tube double-sided radiant furnace type.It has the following characteristics: 1.The operation flexibility is large, because the horizontal tube is easier to obtain the annular flow or the mist flow type than the vertical tube, so the furnace is more adaptable to the operation under various working conditions;2.The pressure drop is small, Due to the average thermal intensity of radiation from the horizontal tube on both sides is 1.5 times the average thermal intensity of the single-sided radiation, and the horizontal length of the furnace tube is only 0.66 times of the single-sided radiation. That is, when the flow velocity in the pipe is the same, the pressure drop is only 66% of single-sided radiation; 3.Equipment investment is small, the furnace tube of the Hydrogenation reaction feed furnace is made of TP321 or TP347 material, and the furnace tube cost more than 40% of the total furnace investment. Therefore,the furnace tube shortens,the weight becomes light and the investment is saved. In the design of the Pre-furnace hydrogen mixing process , the problems of logistic distribution design of furnace and avoiding Furnace tube coking must be solved. The advantage of Pre-furnace hydrogen mixing is that the heat exchange process and the heat exchanger are simple in design,with a high heat transfer coefficient, and the heat exchange area is small. In the case of an accident, the heating furnace is not easily interrupted.
The key to Post-furnace hydrogen mixing is to have enough hydrogen circulation (hydrogen to oil ratio) to carry heat without making the hydrogen furnace outlet temperature too high. The advantages of Post-furnace hydrogen mixing are as follows: 1.The hydrogen is relatively pure and does not coke, so the wall temperature of the furnace tube can be greatly increased, the volume of the heating furnace is reduced, and the steel is saved; 2. The hydrogen is relatively uniform, for the Multi-feed furnace, as long as the resistance of each road is equal, it can be automatically distributed evenly without adjusting valve, saving investment; 3. Heating furnace is easy to design, some heat exchangers can reduce the material level accordingly and save investment.