Distillation technology is widely used in the production of various chemicals, and distillation columns in chemical plants is also one of the more common devices.
In practice, we will encounter such and such problems, today we will give you a summary of the distillation operation of a summary of several common problems, see you have encountered? In the future encounter problems, can refer to the method given by the editor Yo ~ ~ ~
01
Distillation operation how to adjust the pressure of the tower? What are the factors affecting the change in tower pressure?
The operation of any
Distillation Tower, should be controlled within the specified indicators, to adjust other parameters accordingly. Tower pressure fluctuations are too large, it will destroy the whole tower of material balance and gas-liquid balance, so that the product does not reach the required quality.
Therefore, many distillation towers have their specific measures to ensure that the tower pressure is stable within the appropriate range.
For the pressurised tower tower pressure, there are two main methods of adjustment.
1. tower
Condenser for the top of the condenser, tower pressure is generally dependent on the amount of gas phase extraction to regulate. In other conditions remain unchanged, the gas phase extraction volume increases, the tower pressure decreases; the gas phase extraction volume decreases, the tower pressure increases.
2. tower top condenser for the full condenser, tower pressure is mostly by the size of the cold dose to adjust, that is, equivalent to adjust the temperature of the reflux liquid.
Under the premise of other conditions remain unchanged, increase the cold dose, the temperature of the reflux liquid is reduced, the tower pressure is reduced; if the cold dose is reduced, the temperature of the reflux liquid rises, the tower pressure rises.
For the pressure control of the reduced pressure distillation tower, there are two main methods.
1. When the vacuum of the tower is obtained with the aid of an ejector pump, the vacuum of the tower can be adjusted by adjusting the cold dose of the condenser at the top of the tower or the temperature of the refrigerant so as to change the tail gas volume.
When the material to be separated is allowed to come into contact with air, in this control scheme, the steam jet pump works at maximum capacity and the regulating valve is installed in the line to the atmosphere, the size of the regulating valve opening is used to regulate the amount of tail gas pumped through the system, thus achieving the purpose of regulating the vacuum of the tower.
2. When the electric vacuum pump is used to pump the vacuum, the regulating valve is installed on the return line of the vacuum pump and the size of the regulating valve opening is used to regulate the tail gas extraction of the system, thus regulating the vacuum level of the tower.
For the pressure control of the atmospheric pressure tower, there are three main methods as follows.
1. for the tower top pressure in the case of stability requirements are not high, no need to install pressure control system, should be set up in the distillation equipment (condenser or reflux tank) on a through-atmosphere pipeline to ensure that the tower pressure is close to atmospheric pressure.
2. the tower top pressure stability requirements are high or when the separated material can not be in contact with air, the control of the tower top pressure can be used to control the pressure of the pressurised tower tower pressure.
3. The gas phase pressure of the tower kettle is regulated by adjusting the amount of steam heated by the kettle.
02
How can the kettle temperature be adjusted in distillation operations? What are the factors that influence the temperature fluctuations?
The temperature of the kettle is determined by the kettle pressure and the composition of the material. Only by maintaining the required kettle temperature during the distillation process can the product quality be ensured. This is why kettle temperature is one of the most important control indicators in distillation operations.
When the kettle temperature changes, the kettle temperature is usually adjusted to normal by changing the amount of steam heated in the evaporation kettle.
When the kettle temperature is lower than the specified value, the amount of steam should be increased to improve the vapourisation of the kettle liquid, so that the content of the recombination in the kettle liquid increases relatively, the bubble point increases and the kettle temperature increases.
When the kettle temperature is higher than the specified value, the amount of steam should be reduced to reduce the amount of vaporisation of the kettle liquid, so that the content of light components in the kettle liquid increases, the bubble point decreases and the kettle temperature decreases.
There are more reasons for fluctuations in kettle temperature. When the tower pressure rises suddenly, the kettle temperature will rise and then fall again. This is due to the fact that this rise in kettle temperature is caused by the rise in pressure causing a rise in the bubble point of the kettle liquid. As a result, the amount of rising steam in the tower does not increase, but rather decreases due to the increase in pressure.
As a result, the evaporation of the lighter components of the kettle mixture is incomplete, which will lead to a drop in the kettle bubble point and therefore to a subsequent drop in kettle temperature.
Conversely, when the tower pressure suddenly drops, the amount of rising steam in the tower will increase due to the reduction in tower pressure, resulting in a rapid reduction in the liquid level of the tower kettle, so that the heavy components may be carried to the top of the tower. As the components in the kettle liquid become heavier, the bubble point of the kettle liquid rises and so does the kettle temperature. It would appear that the tower pressure is an important factor in causing changes in kettle temperature.
Therefore, the only way to know exactly whether the kettle temperature meets the process requirements is to first control the tower pressure at the required index in the operation, otherwise this will lead to incorrect operation.
The kettle temperature also decreases as the concentration of light components in the feed increases and increases as the concentration of heavy components increases.
In addition, water in the kettle, material polymerisation in the evaporating kettle blocking some of the column pipes, fluctuations in heating steam pressure, failure of the regulating valve, damage to the balance of the material extraction, etc., can cause fluctuations in kettle temperature. Kettle temperature fluctuations, to analyse the causes of fluctuations, to eliminate.
For example, the tower top extraction volume is too small, so that the light components pressed into the tower kettle and cause the kettle temperature to drop. At this time, if you do not increase the tower top extraction, simply increase the amount of tower kettle heating steam, not only on the kettle temperature does not work, in serious cases will also cause liquid flooding.
Another example is that the evaporation kettle's column tube is blocked due to material polymerization, resulting in a drop in kettle temperature, at this time, the equipment should be ordered to overhaul.
03
How to adjust the reflux ratio in the distillation operation?
The reflux ratio is determined according to the separation requirements for the raw material. If the reflux ratio is too large or too small, the economy of the distillation operation and the quality of the product will be affected.
Increasing the reflux ratio increases the concentration of light components in the top product, but reduces the capacity of the tower and increases the consumption of top cooling and kettle heat.
In normal operation should be maintained in the appropriate reflux ratio, to ensure product quality, under the premise of the best economic results. Only in the normal production conditions of the tower is damaged or product quality is not qualified, to adjust the reflux ratio.
For example, the top of the tower product in the recombination content increases, the quality decreases, to increase the appropriate reflux ratio. The tower load (feed) is too low, in order to ensure a certain rate of rising steam in the tower, but also to increase the appropriate reflux ratio.
For large production units, when different types of tower plate structure and rising steam speed requirements and instrumentation design work range and the size of the actual production contradictions, can be appropriate to change the return ratio accordingly.
Another example is the floating valve tower plate, if the processing capacity of only 50-60% of the design capacity, in order to make the floating valve in the appropriate range of work, in order to let the instrumentation measurement range in the appropriate range of work, should be taken to increase the return ratio to ensure the stability of production, which is extremely important for large production units to maintain the necessary stability of production.
There are several ways to adjust the reflux ratio, including the following.
1. reduce the amount of tower top extraction to increase the reflux ratio.
2. the tower condenser for the condenser, can increase the amount of tower coolant to increase the amount of condensate, increase the reflux ratio.
3. forced reflux with reflux intermediate storage tank, can temporarily increase the reflux flow to increase the reflux ratio, but shall not empty the reflux storage tank.
04
How to adjust the differential pressure of the tower in the distillation operation?
Tower pressure difference is the main factor to measure the size of the gas load in the tower, but also to determine the distillation operation of the feed, discharge material is balanced one of the important signs.
In the feed and discharge material to maintain a balance, the reflux ratio is constant, the tower pressure difference is basically constant.
When the normal material balance is disrupted, or the tower temperature, pressure change, will cause the tower to rise steam flow rate change, the tower plate liquid seal height change, causing the tower pressure change.
Distillation operations, to cause changes in tower pressure for the reasons corresponding to the adjustment, commonly used methods are three: 1.
1. In the case of the same amount of feed, with the top of the tower of liquid phase extraction to adjust the tower pressure difference. Product extraction more, then the tower of rising steam flow rate decreases, the tower pressure drop; extraction volume decreases, the tower of rising steam flow rate increases, the tower pressure rise.
2. In the case of constant extraction, the amount of feed to regulate the differential pressure of the tower. Increase the amount of feed, the tower differential pressure rises; reduce the amount of feed, the tower differential pressure falls.
3. Within the limits of the process specification, the differential pressure is adjusted by the change in kettle temperature. Increase the kettle temperature, the tower differential pressure rises; lower the kettle temperature, the tower differential pressure falls.
4. For the equipment problems caused by the differential pressure change, should be specific to the specific problem, serious should stop the maintenance.
05
In the distillation operation how to adjust the tower temperature?
The temperature at the top of the tower is an important factor in determining the quality of the product at the top of the tower. In the premise of the tower pressure remains unchanged, the top temperature increases, the top of the tower products in the recombination content increases, the quality decreases.
There are two main methods of regulating the temperature at the top of the tower.
One is to fix the return flow rate and adjust the return temperature.
One is to fix the reflux temperature and adjust the reflux rate. Due to the increasing size of production units, the method of regulating the return flow rate is widely used in view of the stability of production.
Specific methods of regulating the top temperature of the tower are as follows.
1. Use the return flow rate to control the top temperature. The return flow rate increases, the top temperature decreases, this adjustment method is mostly used in the tower top for the full condenser.
2. when the top of the tower using the refrigerant in the heat transfer process has a phase change, the evaporative pressure of the refrigerant and the top temperature series adjustment to control the top temperature. Evaporation pressure is reduced, the corresponding evaporation temperature is also reduced, causing the top temperature to decrease.
This method can be used to change the return flow when the top condenser is a sub-condenser; it can also be used to change the return temperature when the top condenser has a subcooling effect.
3. when the tower top of the refrigerant in the heat transfer process no phase change, available refrigerant flow and top temperature series adjustment to control the top temperature. If the flow rate increases, the top temperature decreases. This method can change both the return flow rate and the return temperature.
4. top temperature adjustment with the top of the tower condenser heat transfer area. Raise the refrigerant level, the heat transfer area increases, the top temperature decreases. This method can change both the return flow rate and the return temperature.
5. when the distillation section of the material concentration is relatively high, the temperature difference between a certain two plates to adjust the top temperature. The temperature difference increases, the reflux volume increases and the top temperature decreases.
06
What are the reasons why the kettle temperature sometimes does not rise in distillation operations?
Distillation towers are subject to the phenomenon that the kettle temperature does not rise during the start-up temperature rise process and during policy operations.
The reasons why the kettle temperature does not rise during the ramp-up process of the drive may be.
1. failure of the water evacuator (or drainage air stop valve) of the heating system.
2. the return valve of the water lifting station is not open
3. the steam condensate in the heating kettle is not emptied and steam cannot be added to it
4. a large amount of water is present in the material of the tower kettle (water is not soluble with the material)
5. the equipment structure is unreasonable, so that the kettle liquid circulation is obstructed.
6. due to improper operation (heating kettle heating too late or feeding volume is too large, too fierce), resulting in reflux to the tower kettle light component volume is too large, a moment kettle temperature is difficult to mention normal, especially the low temperature liquid phase into the tower, very easy to appear this phenomenon. At this time should change the amount of feed, feed composition or increase the amount of tower top extraction, in order to adjust the operation.
Normal operation, caused by the kettle temperature can not be raised up for the following reasons.
1. blockage of the liquid phase circulation tube of the heating kettle at the bottom of the tower, so that the kettle liquid does not circulate.
2. the material in the column tube of the heating kettle is coking or the column tube is blocked
3. failure of the drain valve.
4. the tower kettle component is too heavy and the existing thermite cannot heat the kettle liquid to the bubble point, resulting in poor circulation of the kettle liquid.
5. a drop in the pressure of the heating kettle thermite.
6. the kettle liquid level is too low or too high.
Source: Chemical Equipment Knowledge
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