1, what is phase and phase equilibrium:
A: phase is a finger in the system with the same physical and chemical properties uniform portion, different phase between often have a phase interface, bar the different phase were opened. System in the number of phases how much and material regardless of the number. Such as water and ice mixed together with water for liquid, ice as solid. In general, the materials in the distillation column are gas and liquid.
In a certain temperature and pressure, if the item exists in the system of two or more phase, material in each phase the relative amount of and material of each component in the in each phase in the concentration does not change over time, we call system in balance. Balance, material or are in constant motion, but, each phase the amount and each component in the concentration does not change over time, when conditions change, will establish a new phase equilibrium, therefore phase equilibrium is sports, relative, rather than static and absolute. For example, in the rectification system, when the gas with higher temperature and the liquid with lower temperature contact with each other, heat and mass transfer should be conducted, and the result is partial condensation of the gas, the formation of liquid high boiling point components concentration increasing. The liquid on the tower plate is partially gasification, and the concentration of the low boiling point component in the formed gas phase increases continuously. But this heat and mass transfer process and not endless, when gas-liquid two-phase balance, its various components of two-phase of the no longer changes with time.
2. What is saturated steam pressure?
A: At a certain temperature, and same substance liquid (or solid-state) in equilibrium steam produced by pressure called saturated vapor pressure, it increases with the increase of temperature. Well known, put it in the cup of water, will by constant evaporation become less and less. If the pure water is put in a sealed container and the air above is taken away, when the water is evaporating continuously, the pressure of the gas phase above the water surface, that is, the pressure of the water vapor, will increase continuously. But, when the temperature when the gas pressure most in stability in a fixed numerical on when the pressure is known as water under this temperature of saturated vapor pressure.
It should be noted that when gas pressure numerical saturated steam pressure is the numeric value, liquid water molecules still constantly gasification, gas water molecule in constantly condensing into a liquid, just due to water gasification speed equal to water vapor condensation of speed, liquid constitute merit no reduction, gas amount did increase, gas and liquid balance state. Therefore, when the pressure of liquid pure substance steam is its saturated steam pressure, the gas-liquid two-phase equilibrium is reached.
3. What is Rectification? What is the principle of rectification?
Answer: conduct several partial vaporization of the liquid mixture, and at the same time, conduct several partial condensation of the generated steam to separate the mixture into required components, which is called rectification.
Why can the liquid mixture be separated into pure or relatively pure components after several times of partial vaporization and several times of partial condensation? For primary vaporization and condensation, due to the different boiling points of components contained in liquid mixture, when it is partly vaporized at a certain temperature, because low boiling points are easy to vaporize, so it is in in the gas phase concentration liquid high, and liquid high boiling point bites the concentration gas high. This change the gas-liquid two-phase composition. When partially condensing the steam from partial vaporization, because the substance with high boiling point is easy to condense, the concentration of the substance with high boiling point in the condensate is higher than that of the gas phase, and for condensing gas low-boiling bites the concentration than condensing liquid medium to high. In this way, after one-time partial vaporization and partial condensation, the mixture gets the initial separation through the change of the concentration of each component. If more times this continue, will eventually in the liquid phase left is basically high boiling point components, in the gas phase left is basically low boiling point components. Thus it can be seen that the mixture can be separated into pure or relatively pure components by multiple partial vaporization and multiple partial condensation simultaneously.
Liquid gasification to absorb heat, gas condensing to produce heat. To the reasonable use heat, we can put gas condensing when heat release supply liquid gasification use when, also is to make gas-liquid two-phase direct contact heat transfer simultaneously mass transfer. In order to meet this requirement, in practice, this multi-Times partial vaporization with multi-Times partial condensation is the process of reverse flow of plate-type devices. So-called countercurrent, is for liquid heat generated temperatures of high gas, bottom-up with the top of the tower for condensation of the temperature lower reflux liquid (rich low boiling point components) reverse flow. The process of heat and mass transfer in the tower is as follows
1) gas-liquid two-phase thermal exchange, use partial vaporization from gas mixture in the heat to heat partial condensation of proceeds of liquid mixture; 2) gas-liquid two-phase in hot swap while qualitative exchange. The low temperature liquid mixture is higher temperature gas mixture heating two partial vaporization. At this point, because volatile difference of (low boiling point bites volatile ability, high boiling point bites volatile ability is poor), low boiling point bites than high boiling point bites volatile multi, the result is that the low boiling point component changes from the liquid phase to the gas phase, and the volatile component in the gas phase increases; similarly, the gas phase mixture with higher temperature, because the liquid mixture with lower temperature is heated, while making oneself partly condensed, also because of the difference of volatilization ability, the component with high boiling point turns from gas phase to liquid phase, and the component with non-Volatilization in liquid phase increases.
The distillation column is composed of several plates. The top of the tower is called Tower top, and the bottom of the tower is called Tower kettle. A tower plate in the tower only conducts partial vaporization and partial condensation once. The more the number of tower plates is, the more times of partial vaporization and partial condensation are, and the better the separation effect is.
Through the whole rectification process, high purity volatile components are finally obtained from the top of the tower, and basically the components obtained from the tower kettle are volatile components.
4, what is dew point?
A: gas mixture in pressure unchanged condition of lower cooling, when the cooling to a certain temperature when the first sign of a tiny droplet, this temperature is called the dew point temperature of the mixture under specified pressure, which is called dew point for short. In dew point temperature gas called saturated gas. From distillation column top steamed steamed out gas temperature, is in dew point temperature. Of note: The first field not pure components, Tower when dew point temperature and gas balanced liquid, its composition with phase equilibrium relationship decision. Thus it can be seen that the dew point of the tower is different for the gas mixture of different compositions.
5, what is make some?
A: liquid mixture under pressure when heated to a certain temperature, appears in the liquid first a small bubble, that just started boiling temperature call the liquid in specified pressure under the bubble point temperature, short make some. In some temperature liquid called saturated liquid, that of distillation tower kettle by temperature. It should be noted that the first small bubble is not a pure component, and its composition is also determined by the relationship of phase equilibrium.
6, what is boiling point?
Answer: When the saturated steam pressure of the pure liquid substance is equal to the external pressure, the liquid will boil, and the temperature at this time is called the boiling point of the liquid under the specified pressure. The boiling point of pure substance changes with the change of external pressure. When the external pressure increases, boiling point lifting, outside pressure decreases, boiling point. For pure material for, under pressure, make some, dew point, boiling point are a numeric value.
7 What is latent heat?
A: Unit weight pure substance in phase change (in no chemical reaction under the condition of material happened phase change, scale phase transition. For example, water forms ice or water vapor forms water vapor, etc., which becomes the phase transformation process .) Process absorption or released hot called latent heat. Such as 1 kilograms water by liquid heating turned into vapour in the process of absorption of heat call water latent heat of vaporization of, common unit for kcal/kilograms. Worth noting is the phase transition temperature and pressure are invariant, otherwise can't call it latent heat. Therefore, when talking about the latent heat value, it is necessary to explain the phase transition process under what temperature and pressure. For example, 1 kilogram of water is vaporized under the pressure of 760mm Hg at 100 degree centigrade, and the latent heat of vaporized water is 539.6 kilocalories. Instead, under this condition, water vapor condensing release the heat of the, called condensation latent heat, numerical and on equal. The latent heat of the mixture can be measured or calculated, and its value is not only related to the nature of the component, but also to the content of the component, which is not a fixed value.
8. What is sensible heat?
A: pure substances does not occur in phase change and chemical reaction conditions, due to temperature change absorption or heat release call sensible heat.
9-what is reflux ratio
Answer: In the process of rectification, the steam generated after the mixed liquid is heated is steamed from the tower top and enters into the tower top condenser. Steam this condensing (or partial condensation) into a liquid, its part condensate return tower along the tray dirty, this part liquid called reflux; another part of the condensate (or not coagulation Steam) from the top of the Tower produced, as the product. Reflux ratio is the weight ratio of the amount of recirculation liquid and the amount of extraction, which is usually expressed as R, that is
R=L/D
R-reflux ratio in the formula
L-in unit time Tower reflux liquid, Kgs/hour.
D-unit time Pineta ding cai reserves, Kgs/hour.
10. What is the minimum reflux ratio?
Answer: Under the specified requirements of separation precision, that is, when the composition of tower top and tower kettle is certain, the reflux ratio will be reduced gradually. At this time, the so-called number of theoretical plates will increase gradually. When reflux ratio reduced to a numerical when required theoretical plates of increased to countless multi-, this reflux ratio numerical, become complete the scheduled separation tasks minimum reflux ratio. Generally, the actual reflux ratio during operation is set to 1.3 ~ of the minimum reflux ratio ~ 2 times.
11. What is total reflux?
Answer: in the rectification operation, stop the tower feeding, the tower kettle discharging and the tower top discharging, and use all the condensate on the tower top as the recirculation liquid to become the whole recirculation. The whole reflux operation is mostly used in the initial start-up of the distillation column, or in the spontaneous circulation operation of the distillation column when the production is abnormal.
12, the most suitable reflux ratio is how determined?
A: To fixed separation requirements process for, when reduce reflux ratio, the running costs (mainly in Tower kettle heating and tower top of cold) will reduce, required plate number will increase, tower investment cost of enlargement; conversely, when increase reflux ratio can reduce the number of plate, but increased the running costs. Therefore, when designing, we should choose the most suitable reflux ratio to minimize the sum of investment cost and operating cost of regular operation under specific economic conditions. The reflux ratio at this time is called the most suitable reflux ratio. The most suitable reflux ratio is 1.3 ~ of the minimum reflux ratio ~ 2 times.
13, what is distillation column pressure drop?
A: so-called distillation column pressure drop, is usually said Tower kettle and tower top pressure difference. To plate column for tray pressure drop mainly is composed of three parts, namely dry plate pressure drop, liquid layer pressure drop and overcome the surface tension of a liquid pressure drop. Tower kettle and the top of the tower pressure difference is the whole column each tray pressure drop combined.
The so-called dry plate pressure drop is the pressure drop generated when the rising gas (or steam) in the distillation tower passes through the tower plate without liquid; when gas through each layer tray on the liquid layer generated when the pressure drop, called liquid layer pressure drop; gas overcome liquid surface tension produced by the pressure drop, called liquid surface tension pressure drop.
For a fixed tower for, in normal operation, Tower pressure drop Main with rising gas flow velocity of the size, experienced showed that tower pressure drop and gas flow rate is proportional to the square of.
14, what is empty tower speed? What is the relationship between it and the hole speed?
Answer: the velocity of empty tower refers to the ratio of the volume of the rising steam of the distillation tower to the sectional area of the tower in unit time, that is, the distance of the rising steam in the tower flowing in unit time. Unit: meter3/Second. m2Or meter/second. Formula is: W = vsaa
In the formula, W-
