Process drawings and installation diagrams of poppet absorber

Contents

Introduction

Poppet Absorption Column Calculation

Calculation Procedure

Select Contact Device Type

Calculation of flow diameter of column nozzles and selection of flanges

Selection of pumps and fans

Calculation of shell-and-tube heat exchanger

Define Data for Calculation

Thermal calculation

Calculation of pipe grids and casing flanges

List of literature

Introduction

Absorption is the process of absorbing gas with a liquid sweater, in which the gas is generated to one degree or another. The reverse process - the release of vegetable gas from the solution - is called desorption.

Two phases participate in absorption processes (absorption, desorption) - liquid and gas and the transition of the substance from the gas phase to the liquid phase during absorption) or, conversely, from the liquid phase to the gas phase (during desorption). Thus, absorption processes are one of the types of mass transfer processes.

In practice, most of the absorption is not carried out by individual gases, but by gas mixtures, the constituents of which (one or more) can be absorbed by the scavenger in noticeable amounts. These constituents are referred to as absorbent components or simply components, and non-absorbent constituents as inert gas.

Liquid phase consists of absorber and absorbed component. In many cases, the scavenger is a solution of an active component that reacts chemically with the absorbed component; moreover, the substance in which the active component is dissolved will be called a solvent.

Inert gas and absorber are carriers of component respectively in gas and liquid phases. With physical absorption (see below), the inert gas and absorber are consumed and not involved in the processes of transition of the component from one phase to another. At chemisorption (see below) the absorber the waste solution merged (after neutralization) in the sewerage can chemically interact with a component of sanitary purification of gases.

The combination of absorption with desorption allows multiple use of the absorber and release the absorbed component in pure form. To do this, the solution after the absorber is sent to desorption, where the component is isolated, and the regenerated (released from the component) solution is again returned to absorption. With such a scheme (circular process), the absorber is not consumed, except for some of its losses, and all the time circulates through the absorber-stripper-absorber system.

In some cases (in the presence of a low-value absorber), in the process of desorption, they refuse to repeatedly use the absorber. The absorber regenerated in the desorber is discharged into the sewer, and fresh absorber is fed into the absorber.

Conditions favourable to desorption are opposite to those conducive to absorption. To perform desorption over the solution, there must be a noticeable pressure of the component so that it can escape into the gas phase. Absorbers in which absorption is accompanied by an irreversible chemical reaction cannot be regenerated by desorption. The regeneration of such absorbers can be carried out chemically.

The fields of application of absorption processes in chemical and mixed industries are very extensive. Some of these areas are listed below:

1. Production of finished product by absorption of gas by liquid. Examples are: absorption of SO3 in the production of sulfuric acid; absorption of HC1 to obtain hydrochloric acid; absorption of nitrogen oxides by water (nitric acid production) or alkaline solutions (nitrate production), etc. At the same time, sorption is carried out without subsequent desorption.

Separation of gas mixtures to isolate one or more valuable components of the mixture. In this case, the absorber used should have as much absorptive capacity as possible with respect to the component to be recovered and as little as possible with respect to other constituents of the gas mixture (selective, or selective, absorption). At the same time, absorption is usually combined with desorption in a circular process. Examples include the absorption of benzene from the coke gas, the absorption of acetylene from the cracking or pyrolysis gases of natural gas, the absorption of butadiene from the contact gas after the deposition of ethyl alcohol, etc.

Cleaning of gas from impurities of harmful components. Such purification is carried out primarily in order to remove impurities that are not permissible during further processing of gases (for example, purification of petroleum and coke gases from H2S, purification of the nitrogen-hydrogen mixture for the synthesis of ammonia from CO2 and CO, drying of sulfur dioxide in the production of contact sulfuric acid, etc.). In addition, sanitary cleaning of exhaust gases released into the atmosphere is carried out (for example, cleaning of flue gases from SO2; purification from C12 abgas after condensation of liquid chlorine; purification from fluorine compounds of gases released during the production of mineral fertilizers, etc.).

In this case, the extracted component is usually used, so it is isolated by desorption or sent to the appropriate processing. Sometimes, if the amount of the extracted component is very small and the absorber is not of value, the solution after absorption is dumped into the sewer.

4. Capture of valuable components from the gas mixture to prevent their loss, as well as by sanitary applications, for example, recovery of volatile solvents (alcohols, ketones, ethers, etc.).

It should be noted that for the separation of gas mixtures, the purification of gases and the capture of valuable components, along with absorption, other methods are used: adsorption, deep cooling, etc. The choice of one or another method is determined by technical and economic considerations. Generally, absorption is preferred where very complete removal of the component is not required.

During absorption processes, mass exchange occurs on top of phase contact. Therefore, absorption devices should have a developed contact surface between gas and liquid. Based on the method of creating this surface, absorption devices can be divided into the following groups:

1. Surface absorbers in which the surface of contact between phases is a liquid mirror (surface absorbers themselves) or the surface of the current liquid film (film sorbers). The same group includes nozzle absorbers, in which liquid flows along the surface of a nozzle loaded into the absorber from bodies of various shapes (rings, lump material, etc.), and mechanical film absorbers (p. 321). For surface absorbers, the contact surface is determined to a certain extent by the geometric surface of the absorber elements (for example, the nozzle), although in many cases it is not equal to it.

2. Bubbling absorbers, in which the contact surface is developed by flows of gas distributed in the liquid in the form of bubbles and jets. Such gas flow (bubbling) is carried out by its transmission through the device (continuous bubbling) filled with liquid or in devices of columned type from various type by plates. A similar nature of gas-liquid interaction is also observed in nozzle absorbers with a flooded nozzle.

The same group includes bubble absorbers with mixing of liquid by mechanical stirrers. In bubbling absorbers, the upper contact is determined by the hydrodynamic mode (gas and liquid flow rates).

c) Spray absorbers in which the contact surface is formed by spraying the liquid in the gas mass into fine droplets. Contact surface is determined by hydrodynamic mode (fluid flow). This group includes absorbers in which liquid dust is carried out by nozzles (nozzle, or overflow, absorbers), in the flow of gas moving at a high speed (speed ramjet atomizing absorbers) or rotating mechanical devices (mechanical atomizing absorbers).

The given classification of absorption devices is conditional, since it reflects not so much the design of the device as the nature of the contact surface. The same type of apparatus, depending on the working conditions, may also be in different groups. For example, nozzle absorbers can operate in both film and bubble modes. In devices with bubbling trays, modes are possible when significant spraying of liquid occurs and the contact surface is formed mainly by drops.

Of the various types of devices, nozzle and bubble poppet absorbers are currently the most common. When taking the absorber type, it is necessary to proceed on a case-by-case basis from the physicochemical conditions of the process, taking into account technical and economic factors.

The main dimensions of the absorber (for example, diameter and height) are determined by calculating based on the given operating conditions (productivity, the required degree of extraction of the component, etc.). Calculation requires information on process static and kinetics. Static data are found from reference tables, calculated using thermodynamic parameters or determined experimentally. The data on kinetics largely depend on the type of apparatus and its mode of operation. The most reliable are the results of experiments conducted under the same conditions. In some cases, such data are absent and you have to resort to calculation or experiments.

Currently, there is not yet a quite reliable method that allows you to determine the mass transfer coefficient by calculating either on the basis of laboratory or model experiments. However, for some types of devices, you can find mass transfer coefficients with precisely high accuracy using calculation or relatively simple experiments.