Part II: Introduction to the Methods of Chemical Project Development
Equipment Selection
Based on the work of the chemist, the process engineer's task is to select the most suitable industrial reactor type or selection. The selection process includes a combination of factors. For example, the targets that can be achieved, equipment investment, energy and operating costs, equipment manufacturing and materials, environmental protection and safety, operation and control, as well as the quality of personnel.
Process amplification
The so-called amplification, is based on the selected reactor type, through experimentation or other means available to all, in the shortest possible time, with the least investment, the amplification of the equipment for equipment engineers to buy or manufacture equipment used.
One of the hallmarks of the modern process industry is the large-scale equipment, because the process industry to obtain the benefits mainly rely on the large-scale equipment, rather than relying on the increase in the number of equipment to achieve. The chemical industry belongs to the process industry, with the progress of technology, the chemical industry is increasing in size. For example, the production capacity of a single ethylene plant has increased from 300,000 tons/year to 450,000 tons/year, and then to 600,000 tons/year or even 1 million tons/year. Another example is methanol, the capacity of a single unit from 100,000 tons/year to 400,000 tons/year, and then increased to 1 million tons/year or even 2 million tons/year. In short, the scale is constantly expanding.
For a long time, as far as the chemical industry is concerned, the small test held up why can not be rapidly industrialized, as far as technology is concerned, to the chemical reaction as the characteristics of the project, the understanding of the law of amplification and the use of chemical amplification technology in order to achieve the scale of the production of the key, but also China and the developed countries is an important gap. （
In order to truly face international competition, we must pay attention to the process of amplification, the construction of large-scale chemical plants.
The chemical process has the following two types, one is the transfer process, including transmission, heat transfer and mass transfer process, belongs to the physical process without changes in the composition of the material; twenty chemical reaction process that, belongs to the chemical process with component changes. These processes are realized in the equipment, so the process amplification is the amplification of the equipment capacity.
Process amplification generally go through the stages
(1) laboratory research stage;
(2) small amount of trial production stage;
(3) conceptual design according to the predetermined scale of the process;
(4) pilot, focusing on solving the problems encountered in the conceptual design;
(5) preparation of the process software package;
(6) engineering design at the required scale;
(7) construction and commissioning of industrial units.
Methods of process scaling up
1. Full process scaling up step by step
One of the most traditional methods is to realize large-scale industrial production step by step by starting from small-scale tests, slightly larger-scale tests, intermediate tests, and expanded intermediate tests. This process of scaling up through multiple levels of testing is necessarily time-consuming and costly. In the early days of the process industry, empirical scale-up was almost the only method. Process development technology today, purely empirical amplification is obviously not very desirable, but for some overly complex, little-understood processes, sometimes have to resort to
empirical amplification.
2. Mathematical simulation method of amplification
The establishment of mathematical models (a set of mathematical equations) to describe the process, and through the different scales of experimentation in order to determine the parameters of the model, and then through the computer simulation of the process of large-scale various behaviors, in order to determine the guidelines for amplification. This kind of scaling up is theoretically reasonable, however, it has been shown that there are not many successful examples of scaling up purely by mathematical simulation, for the following reasons:
(1) because the actual processes are usually extremely complex, and people's understanding of them
is often not systematic and comprehensive enough, thus making it difficult for the mathematical models to be
established;
(2) even if the complex actual processes are fully understood, they may be difficult to establish; and
(2) even if they have been fully understood, the actual processes are not systematic and comprehensive enough, so that it is difficult to build mathematical models. Even if the complexity of the actual process has been fully understood, the establishment of mathematical models must make a number of simplifying assumptions, and thus in order to facilitate the description, it is likely to get an oversimplified model;
(3) the reliability of the experimentally determined model parameters are often subject to the limitations of the experimental means and experimental process of the interference of noise, and therefore there is a greater or lesser degree of uncertainty in the model parameters.
Because the mathematical simulation method of amplification can only be applied to people's understanding of the process has been quite thorough, the determination of parameters is quite reliable occasions. With people's understanding of the level of test methods and computer applications to improve the level of mathematical models and computers, the establishment of the whole process of mathematical model for amplification, there is no lack of successful examples, such as low-pressure method of methanol is an example. Admittedly, the use of mathematical models still need to do some auxiliary experiments as a complementary and verification, but the use of mathematical simulation amplification is the process of amplification of the most effective way to save time and money.
Process amplification should pay attention to the problem
1. must ensure that the economic rationality of the equipment amplification and indicators of the advanced and system tuning
Equipment amplification must also ensure that the economic rationality and indicators of the advanced. Often after enlargement, there are some indicators tend to be reasonable, such as energy consumption can generally be reduced. But some other indicators, due to the large-scale after, such as the reaction product yield tends to be reduced, the temperature and other operating conditions are not easy to control, which is often referred to as the "amplification effect". This is often referred to as the "amplification effect", and the amplification effect is considered to be a disadvantage. An important task for us is to keep these indicators as high as possible even after the process has been scaled up. Another reality is that an actual process is usually not optimally operated. This is due to the complexity of the process and the limitations of people's cognitive abilities, not to mention the fact that some parameters of the process change over time.
The above is only true for a single piece of equipment, because a process is a complete flow of multiple pieces of equipment, i.e., it is a system. In this sense, the process amplification should be a system amplification, the amplification of a single device in the system is not equal to the system amplification, so it must be system optimization. Therefore, the complete process amplification should include equipment amplification and system tuning.
2. pilot scale determination
Why pilot? Need to verify the small test law, but more importantly, to solve the problems that may be encountered in large production units, so what problems may be encountered in large production units? For a new product, not yet industrialized is unable to answer, in order to anticipate as much as possible the problems that may be encountered, is to first engage in a conceptual design, the conceptual design of the scale should be the size of the expected industrial unit, in the process of conceptual design, can be applied to the existing process experience and digestion of publicly available literature, but in the process of designing the hypothetical industrial scale, you will still encounter many problems (such as data, materials, control methods, reaction endpoint control, material balance, etc.), which prevent the conceptual design from proceeding further, and it is precisely these problems that have to be solved in the pilot test. In order to solve or clarify these issues, may require the pilot must reach a certain scale, which is the pilot scale to determine the basis and the pilot design should be achieved to solve these problems in the way.
3. To obtain engineering test data as one of the objectives of the pilot test
Many development projects do not pay attention to the development of basic data, will affect the operation of industrial installations, a practical example is a device is completed, the reactor does not react to the material, while the reaction conditions, the raw materials are consistent with the requirements of the laboratory, the impact of the work period of up to six months. After many tests to identify the comparison, the stirrer uses a copper shaft tile, copper ions will prevent the reaction, but this point, in the small test is not presented as relevant data, so that the design did not pay attention to this point and affect the production. Another example is the conditions of crystallization, the conditions affecting the size of the grain is what factors, if you can do a good job of the relevant data on the amplification is very useful. Another example is the gas-liquid equilibrium data of multi-component, often can not be found, it is necessary to measure the whole component of the reaction to obtain. Another example is the determination and control of the reaction endpoints, etc., these are impossible to do a small test, while the test must be done.
4. Material test
The corrosion resistance test of the material is the main task of the pilot test, about which I believe that most of the corrosion manuals and suppliers can get enough information. In addition, special attention should be paid to the presence of a small number of ions, the role of corrosion, such as the effect of metal ions, the effect of halogens, thermal stress, corrosion stress, etc., should be measured or done hanging test, pay special attention to the "actual" medium, rather than a pure medium. Such as acetic acid medium corrosive in the relevant manuals can be found, but acetic acid contains traces of halogens, in the end, how much corrosive, there is no readily available information, it must be the actual medium for research.
5. Pay attention to the selection of key equipment
A general pump, fan, compressor amplification should not be a major problem, distillation, separation of the amplification, can also be solved at present. But the reactor is the focus of the test to be resolved, what type of reactor is good for heat transfer, reaction temperature control, catalyst life, poisoning, regeneration, through the test to be clarified, to provide a basis for amplification of the design. In addition, special such as drying type, especially slurry, should be selected by the test equipment. Another example of filtration, seemingly simple and actually different materials filter type selection, filter cloth selection, should also be determined by the test to avoid engineering rework.
6. The study of raw materials, intermediate and finished products
Generally, the laboratory stage only reagent-grade products as raw materials, as far as possible, the pilot test using industrial-grade products as raw materials, a small number of impurities on product quality, what is the impact of what method of pretreatment, these issues should be clarified in the pilot test. Some may want to dehydration, some may want to pre-distillation. Small test quantity is small, some impurities are not necessarily separated out, the number of pilot tests, as much as possible for the whole analysis, the intermediates, finished products, residues, composition, composition clear, conducive to do the balance of materials and the whole process for the overall analysis.
7. Safety, production, environmental protection
Should collect all raw materials, intermediates and finished products of the MSDS, the chemical properties of the material, a comprehensive understanding of the toxicity, and to take the appropriate protection and fire, safety measures.
The composition and treatment of discharges, slag, waste liquids and waste water are carefully studied to guide the engineering design.
8. Pay attention to the amplification process, researchers and engineering designers close cooperation
Because the researchers are mainly in the mechanism of theoretical research more, engineering designers will be more consideration of the process layout system amplification and other issues. Utilizing their respective strengths is conducive to the smooth progress of the work.
Summary:
In short, the amplification of the chemical process is a new product development process must be the way, is the scientific research into productivity after all the way. This link is handled well, you can accelerate the industrialization of new products. Process amplification process, can not stay in the product out, through the process; also not only the pursuit of equipment and unit process optimization, but ultimately the pursuit of system-wide optimization.
The laboratory stage of the small test is exploratory, focusing on the study of mechanism, feasibility, physical data, check (measurement) to find out the process route. This is mainly researchers, engineers to participate in the small test on the basis of the conceptual design of the target scale, from which to identify the pilot (scale-up) need to solve the problem, used to guide the design of the pilot plant. Conceptual design can be completed by the researchers, can also be completed by the engineering staff, of course, a combination of the two *** with better. Pilot plant size and process determination, should be able to meet the needs of the conceptual design, during which must be done in close cooperation with engineering and research personnel. Pilot should be the whole process, otherwise it will not meet the requirements. As can draw on readily available effective unit process and carry out computer simulation, and does not mechanically require the full process, to avoid low-level duplication, focus on solving difficult problems. On the basis of the completion of the pilot test to complete the preparation of software packages, basic design, and then engineering design. Of course, in each of the above stages to do technical and economic analysis to determine the prospects of the project, feasibility.