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Spray tower design standard reference

Views: 11     Author: Xicheng EP LTD     Publish Time: 2022-08-09      Origin: Xicheng EP LTD

To choose a suitable spray tower type, we must go through investigation and research, fully understand the use conditions, and choose a reasonable tower type with better characteristics.
Generally speaking, there are many choices of spray tower types that meet the requirements of production tasks at the same time, but they should be comprehensively considered from the economic point of view, production experience and specific conditions. Here are some of the factors to consider when choosing.

Spray tower design

1.Factors related to physical properties

  1. The logistics system is easy to start foam, and a packed tower should be used. Because it is easy to cause serious isothermal fire zone in the plate tower, it will reach the pan tower, which will affect the separation efficiency.

  2. Materials with floating solids and residues, or materials that are easy to scale, such as large aperture sieve tray towers, cross-type float valves and bubble towers, etc. Packed towers will produce male plugs that are difficult to clean.

  3. High viscosity: Packing tower is used for material treasure. The mass transfer effect of bubbling in the tray column is too poor.

  4. Packed towers should be used for the medium with corrosive properties, because it should be made of corrosion-resistant materials, or a non-overflow sieve tray tower with a simple structure in the tray tower can be used.

  5. For systems that emit heat or need to add heat during the treatment process, a plate tower should be used. Of course, the packing can also be divided into towers or sections, and the towers (sections) can be set with coolers, but the structure is more complicated.

2.Factors related to farming conditions

  1. The mass transfer rate is controlled by the gas phase, and a packed tower should be used, because the gas phase is indiscriminately moving in the packed tower, and the liquid phase is dispersed into a film-like flow. The milk mass transfer trace ice is controlled by the liquid phase, and the tray tower is used, because the liquid phase is flowing in the tray Spray tower, and the gas phase is dispersed into bubbles.

  2. When the liquid volume of the processing system is smaller than the LV, a plate column should be used.

  3. When the operating flexibility is required to be large, the treasure adopts the floating Spray tower and the bubble tower. Packed columns and non-overflow sieve tray columns are less elastic.

  4. For the absorption process accompanied by a chemical reaction (especially when the reaction is not too rapid), it is more advantageous to use a plate column, because the residence time of the liquid in the plate column is long, and the reaction is easier to control, which is beneficial to the absorption process. 

  5. Plate towers should be used for systems with large gas-phase processing capacity, and packed towers are suitable for small ones. Due to the high price of large plate towers and the cheaper packed towers of small towers, generally, packed towers should be used when the diameter of the Spray tower is less than 800mm in diameter.

The following are some key points to consider when designing a SPRAY TOWER, mainly including:

The smaller the airflow velocity of the hollow spray dust collector, the better the absorption efficiency, generally 1.0-~1.5m/s.

Filler layer thickness

In the cross-flow simulated packing scrubber, the thickness of the packing layer clamped by the two layers of screens is generally less than 0.6m, and the maximum is 1.8m.

Spray section: from the spray layer (the top layer of the nozzle to the upper mouth of the air inlet pipe, the gas-liquid contact mass transfer in this section is the main section of the Spray tower. Hydrogen fluoride is a hydrophilic gas, and mass transfer can be achieved in an instant. Completed. However, in actual operation, the length of this section is still a major factor due to the influence of the spraying liquid state and the distribution of gas in the cross-section of the body. It is thought that in this section, the cross-section of the Spray tower is full of droplets , the free surface is greatly reduced, so that the actual velocity of the airflow increases many times, so the contact time cannot be calculated according to the superficial velocity.

Dehydration (defogging) section: the upper part of the nozzle is the dehydration section, which is used to make large droplets fall by their own weight, and a mist eliminator is installed in it to remove small droplets, so that the gas and liquid can be better separated. There is no unified calculation method for the height of the Spray tower. Generally, it is selected with reference to the diameter. The ratio of height to diameter (H/D) is within the range of 4-7, and the spray section accounts for more than 1/2 of the total height. Turbulence Spray tower gas purifier, the packing layer can be floated. The Spray tower is filled with lightweight hollow (or solid) pellets made of polyethylene, polypropylene, foamed pulp styrene or hollow rubber as filler, and the density of the pellets should be less than that of the washing liquid. Under the action of a certain airflow velocity, the small balls in the Spray tower continuously move in full flow, and the dust particles are captured by the gas jet in the foam layer of the turbulent motion.

When the turbulent Spray tower purifier is used for dust removal, the limit speed of air flow in the tower is 5~6m/s, and the liquid-gas ratio is 0.5~0.7L/m3:

Select the appropriate diameter of the filler ball, according to the experiment, it is the best efficiency to use the filler ball with a diameter of 20-40mm and a density of 200-300kg/m to purify the dust-laden gas. The quotient H of the static bed of the packing pellets is about 5~8 times the diameter of the spherical packing, and the maximum static bed height Hu (ma should be derived from the relationship of Hw/D 1 . When the flow Spray tower is multi-layered, the upper The distance between the support sieve plate of one layer and the support sieve plate of the next layer is 1~1.5m, and the distance between the limit grid plate and the support mixing plate is 0.8-0.9m.

Number of nozzles

The function of the nozzle is to spray the washing liquid into fine droplets. The reasonable structure of the spray can fully atomize the washing liquid and increase the gas-liquid contact area. On the contrary, all the huge Spray towers and the washing liquid are not sprayed well, and the gas-liquid contact area is still very small, which affects the purification efficiency of the equipment. The ideal nozzle is as follows:

  1. The ejected droplets are small, and the size of the droplets depends on the nozzle structure and the pressure of the washing liquid.

  2. Large cone angle of the ejected liquid The larger the cone angle, the larger the coverage area, and the entire section of the Spray tower will be covered not far from the ejection gas. A whirlpool is installed in the pan, so that the liquid not only moves in the forward direction, but also rotates, which helps to spread the sprayed liquid and disperse the sprayed liquid into fine mist.

  3. The promised hydraulic pressure is small. If the hydraulic pressure is small, the power dissipation is low.

  4. The spraying ability is large, and the theoretical calculation of spraying ability is in practical engineering,

The chimneys should be evenly arranged on the upper and lower sides to ensure that the spray density of the new and upper points is the same, and there is no cavity or uneven density. The smaller the airflow speed of the hollow spray dust collector, the better the absorption efficiency, generally 1.0-~1.5m/s.

design a wet scrubber

Calculation of Spray tower diameter

The diameter of the Spray tower is determined by the required processing gas volume per hour and the passing speed of the gas in the tower.

Gas-liquid ratio selection

The water-gas ratio is the most closely related control condition to the purification efficiency, and its unit is kg liquid/m³. When other conditions remain unchanged, the larger the water-gas ratio, the higher the purification efficiency, especially when the water-gas ratio is below 0.5 , the purification efficiency increases sharply with the increase of the water-air ratio. This is because the amount of water cannot meet the absorption requirements, but after it increases to a certain extent, it is no longer necessary to increase the amount of spray, but it will increase the amount of air entrainment. Tests have determined that the water-gas ratio of the Spray tower is 0.7-0.9
appropriate. Of course, this is related to many conditions. For example, the atomization of the washing liquid is not good. Even if the water vapor is relatively large, the mass transfer effect is still not good.

Pump selection

The selection basis of the water pump should be based on the technological process, water supply and drainage requirements, and should be considered from five aspects, namely the liquid delivery volume, loading head, liquid properties, pipeline layout and operating conditions, etc.

  1. Flow rate is one of the important performance data of water pump selection, which is directly related to the production capacity and conveying capacity of the entire device. For example, in the process design of the Design Institute, the normal, minimum and maximum flow rates of the pump can be calculated. When selecting a pump, take the maximum flow rate as the basis, and take into account the normal flow rate. When there is no maximum flow rate, 1.1 letter of the normal flow rate can usually be taken as the maximum flow rate.

  2. The head required by the device system is another important performance data for pump selection. Generally, the head should be enlarged by 5%-10% margin for selection.

  3. Liquid properties, including the name of the liquid medium, physical properties, chemical properties and other properties. The physical properties include temperature. Density d, viscosity u, solid particle diameter and gas content in the medium, etc., which involve the head of the system, the calculation of effective NPSH and the type of suitable pump: chemical properties, mainly refers to the chemical corrosiveness and toxicity of the liquid medium, It is an important basis for selecting pump materials and selecting which type of shaft seal.

  4. The piping layout conditions of the device system refer to the liquid feeding height, the liquid feeding distance from the brine feeding direction, the lowest liquid level on the suction side, the highest liquid level on the discharge side, etc. - some data and pipe specifications and their lengths, materials, and pipe fitting specifications , quantity, etc., in order to calculate the head of the tie-comb and check the NPSH.

  5. There are many operating conditions, such as liquid operator saturated steam force P, suction side pressure PS (absolute), discharge side container pressure pz, altitude, ambient temperature, whether the operation is intermittent or continuous, and the position of the pump is fixed It is still removable, choose the specific operation of the water pump

Water tank pump

According to the principle of pump selection and the basic conditions of remote type, the specific operations are as follows:

  1. According to the arrangement of the device, terrain conditions, water level conditions, and remote rotation conditions, determine the selection of horizontal, vertical and other types (pipeline type, submersible type, submerged type, non-blocking type, self-priming type, gear type, etc.) of the pump.

  2. According to the properties of the liquid medium, determine the clean water pump, hot water pump or oil pump, chemical pump or corrosion-resistant pump or impurity pump, or use a non-clogging pump. The pump installed in the explosion area should use the corresponding explosion-proof motor according to the level of the explosion area.

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