-To print this articleChemical-technological process carried out to transform raw materials into marketable products. The system of devices of different functional purpose, interconnected material and energy flows and operating as a single entity for the purpose of production of marketable products of a given quality, called chemical-technological system (XTC). The number of devices, the sequence of their participation in the production process, materials and heat flows between the devices describes the structure of CTS. The structure of CTS form its constituent elements and relationships between them. Elements of the CTS are separate devices. The connections between the elements are in the form of pipelines, that carry the material and heat flows.
Each element of the CTS performs certain functions for the transformation parameters, of incoming flows and outgoing flows options. The state parameters of the process streams are the flow, temperature, pressure, the concentration of components, etc. Size, equal to the number of parameters of the process stream is called the stream parametrically.
Constructional and technological parameters of the elements of the CTS allow you to control the process. Therefore they are also called control parameters.
Communication between devices located inside call CTS internal links, communication between devices of various CTS and the external environment – external links. The characteristics of the elements of the CTS and the nature of technological linkages depends on the quality of the functioning of CTS. The efficiency of CTS can be improved:
- by changing technological linkages between existing in the system;
- by improving the functioning of the basic elements of CTS.
The structure of CTS is depicted with the help of various schemes
Preparation and organization of the HTP begins with the choice of chemical scheme of the process, ie. scheme of transformation of raw materials to the desired product, presented in the form of corresponding equations of chemical reactions. Chemical schemes are developed based on the analysis of possible directions of synthesis based on the properties of raw materials, the quality requirements of the product, the availability of energy resources, etc. The decisive criterion in the choice of scheme is the efficiency of production according to one method over the other. For example, phosphoric acid can be derived from fluorapatite three possible schemes: decomposition of raw materials with sulfuric acid, decomposition of raw materials nitric acid and electrothermal method using phosphorus pentoxide.
In this case, the most economical method for sulfuric acid decomposition, ie. the chemical scheme:
Sa5F(PO4)3 +5H2SO4 =3H3PO4 + 5CaSO4 + HF
H2SO4
Sa5F(PO4)3 HNO3 H3PO4
C
O2 H2In
P P2O5
Rice. 1.6.1 Possible schemes of production of phosphoric acid
Based on the chosen chemical scheme prepared structural scheme CTS. Structural diagram expresses the relationship between fundamental chemical, physical and mechanical operations, presented in a cosmetic. The flow diagram all the elements of the CTS are graphically presented in the form of blocks, with multiple inputs and outputs of material and heat flows. Technological communication between the blocks indicated by lines with arrows, indicating the direction of flow. The structural scheme gives a General idea about CTS, and contains almost no quantitative information about the flows, nor about the features of the elements of XTC.
So, in the example above chemical scheme of the production of phosphoric acid structural diagram looks like this:
Part H3PO4
Sa5F(PO4)3 H3PO4
N2In
breed
HF phosphogypsum Sao4
Fig.1.6.2 block diagram of phosphoric acid production
Structural scheme allows a first approximation to assess the feasibility and efficiency of the selected CTS.
The technological scheme is called the totality of all stages of the HTP, material and expressed in devices, machines, communications. It is, therefore, sequential image or description of processes and devices, components of the chemical-technological system. Unlike structural diagram, on the basis of which it is developed, in the technological diagram of the devices shown in the drawings, simplistically representing their appearance and less, the internal structure. The machines are linked in their production flows, depicted as lines with arrows, the pointing direction of flow. The images are supplemented with brief information about the chemical composition of the feedstock and reaction products. However, simultaneously operating devices of the same purpose and design (for example, battery evaporators) portrayed in the form of a single apparatus.
Depending on the purpose of technological schemes are varying degrees of detail.
Communication between the machines come in various types. Technological and structural scheme can be implemented in production in several versions:
1. Serial communication. Characterized by the fact, what emerges from the preceding element of the stream is being input to the subsequent device, and all processing flows through each element at most once. This type of connection is the most common. This is a circuit with open circuit, are a number of devices, through which all reacting substances are held only once (flow diagram). They are used in the production of, based on irreversible or reversible, but reaching a high yield of product, processes, in which the equilibrium conditions can be achieved a high degree of transformation of raw materials without isolation of the target product from the reaction mixture, (for example, production of acetylene, of superphosphate).
Serial communication is also used, when it is necessary to increase the degree of conversion, selectivity, the speed of the process due to the partitioning of the reaction zones, to create the optimal temperature regime, to provide interim withdrawal of the reaction products. If the degree of conversion in a single unit small, you have to consistently add several similar phones. A typical example of serial connection is a cascade of rectors of mixing, enhance the speed of the process by increasing the driving force of the process on sequential partitioning of the zone.
Diagram of open circuit
The scheme includes three similar lines: production of reagent L from A and b, production of reagent M from C and D and the production of the final product R from L and M.
A® A+B AB AND, In, To
In®
L M+L R R
S, L, M
C+D DM M
D D MP N
Rice. 1.6.3 Diagram of open circuit
1 –mixing of reagents, 2– chemical transformations, 3– separation of the reaction products,
To, N, S –by-products
An example of a heterogeneous process with an open circuit in the gas phase, ongoing in the series connected devices, can serve as the technological scheme of separation of the acid absorption of nitrous gases in the production of diluted nitric acid. Under the open circuit to build production, includes irreversible and reversible processes, going with the big yield.
2. Series-bypass technological communication.
This type of communication, often called bypass, characterized by the fact, what part of the process stream passes one or more vehicles in the course of the technological scheme. The bypass allows you to effectively manage temperature and concentration modes of operation of the apparatus. It is used, for example, at the adiabatic carrying out exothermic chemical reactions together with a serial connection elements of the chemical conversion. By bypassing the cold flow of raw materials, high flow temperature of the reactants at the outlet of the adiabatic reactor is reduced, the concentration of the reacting raw materials at the exit of the adiabatic reactor is increased. The bypass can also be used to control the temperature at the outlet of heat exchanger node.
3. Parallel process communication.
Parallel process communication is used to improve performance, increasing the range of products, derived from the same raw materials, security and protection CTS. As a rule, parallel process communication is used to improve the functioning of CTS, consisting of series-mounted devices, having under the terms of the various scaling limit power. In this case, the power of the entire system will be determined by the element with the least capacity. To increase the capacity of the XTC install two or Bode the same parallel element, the total power equal to the most productive element.
If on the basis of one original substance get several intermediate products, which can then be used to produce the same desired product, we simultaneously establish several different elements, working in different modes.
4. Return neziklicescoy technological communication.
If the product yield in a single unit is 4-5 % (synthesis of alcohols) or to 20% (the synthesis of ammonia) and reacting the mixture contains only a small number of (inert) impurities, it is advisable to build the production for the cyclic scheme.
Return process communication is characterized by the presence of the reverse process stream, connecting the output of any other element to the input of one of the previous elements of XTC. This type of communication (öilichevskaya scheme) provides repeated return to the same machine all the reacting mass or one of the phases in the heterogeneous process until a predetermined degree of conversion of the starting materials (rice. 4.4). The circulation scheme is used in the production of, based on reversible processes, ie. in which with the current mode and parameter values (temperature, pressure, the catalyst) the equilibrium conditions cannot be achieved in a single pass through the apparatus quite high degree of transformation of raw materials (for example, the production of ammonia, methanol). Application of reverse technological communication makes better use of raw materials during the operation of the reactors in terms of thermal or thermodynamic restrictions on the degree of conversion of.