Abstract
The objective of this paper is to present the conceptual design considerations that should be integrated into polymerization reactors to reduce risks such as toxicity, flammability, and high pressure. This ranges from optimization, decoupling, and design by which conceptual decomposition of the batch reactor falls under distinct characteristics. In this paper the notions of flexibility controllability, hazardous practices and safety design for polymerization batch reactors will be presented.
Following previous studies that have been done on polymerization reactors, this paper will address some of the concerns pertaining to design in literature review. The research is important because the chemical processes that produce polymeric materials in various sectors of the economy are widespread across a number of industries such as agriculture, food, cosmetics, and skin among others. Yet they present hazardous risks and have potential of resulting in catastrophic events. Assessments on potential hazards posed by batch reactors should be carried out. Furthermore, in batch reactors all reactants are added at the start hence the potential for high pressure and temperature. Associated with overheating. Thermal runaway particularly is a big problem that arises from unsteady state in the polymerization batch reactors. Therefore this paper will address the conceptual factors that should be incorporated in the design to counter challenges presented by potential risks.
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Introduction
Over 300 products are produced by the International Specialty Products (ISP) for use in industries such as pharmaceuticals, hair, skin, agriculture, food processing, and adhesive markets among others. The diverse products include a range of either monomers or polymers that are produced through batch, continuous and semi-continuous processes. ISP is committed to supporting the development of effective approaches and that take control of risks involved in the process of manufacturing. One of the important commitments is the recognition that device designs help contain manufacturing equipment and protect it from overpressure. Usually, the containment design is done from a standpoint of health and safety and takes into consideration an analysis of toxicity, order leakages, flammability and corrosiveness (Leung & Greenfield, 2006). If the analysis indicates that there is a potential risk, reactors are further designed to minimize the risks. Among additional systems that can be addressed include containment design systems. This paper addresses important factors that should be taken into consideration in the design of containment systems for batch polymerization reactors.
As an umbrella term, a batch refers to a type of vessel that is used in industries in processes such as product mixing, chemical reactions, batch distillation, crystallization, liquid extraction and polymerization (Schork, 2017). Typically, a batch is comprised of a storage tank that has an agitator, integral cooling and heating system which vary in size from one up to 15,000 liters. Batch reactors are fabricated either in steel, glass, or exotic alloy. Processes involving batch reactors are very critical in the chemical industry. Because of their versatility and flexibility, batch reactors are can continuously carry out a series of reactions without the need to break containment.
Notably, polymerization has had a growing trend in the chemical industry over the years. Approximately over 100 billion polymer materials are produced annually and this figure is set to increase in the future. With such a huge scale of production, improvements in the containment design are very critical in the chemical processing industry. Various polymeric products are made in various batch reactors at a manufacturing site. It is also worth noting that most of these polymeric products are of low volume, designed in such a manner that they are able to perform a specific function. Due to this characteristic, a batch of reactors is the most prevalent model. For the design of the batch reactors, capital and reduced costs of operation are not the main design objective. Instead the ability of batch reactors to produce high-quality polymeric products is. Normally, quality is determined during the architecture stage and not post-polymerization. This has created the need for efficient design of batch reactors.
Polymers produced are usually both homo and copolymers. Typically they are run as solution polymerization reactions. Low molecular weight solvents such as ethanol and propanol and monomers such as vinyl acetate and vinylpyrrolidone are used in the process (Hreiz, Latifi & Roche, 2015). Usually the reactions are exothermic, which could be potentially risky in terms of high temperatures and high pressures that could be beyond what the batch reactors are capable of containing. This paper will reveal the need for updating relief systems for polymerization reactors in the chemical processing industry.
In a recent study regarding the containment design for multiple batch reactors, findings revealed that a containment vessel was necessary to mitigate the risks that come with the process of polymerization. In the scenario, the batch polymerization rectors were fire-imposed runaway of a normal process batch. Based on the DIER method, calculations of the fire ring were made to determine if they which gallon it would encompass (Geraci et al, 2015 ). For that study, the containment research was designed such that it could accommodate relief from either the 1000 or 4000-gallon batch reactors. In the process of designing the batch reactors, it is important to consider the kind of system one is dealing with; can either be active or passive. In most batch reactors the pool is usually passive hence the ability to offer low cost and reliable methods. Usually the design is based on the fact that it has a fluid that is capable of cooling the runway reaction material to counter the risk of flammability. Hot discharges from the relief discharge are supposed to be released to the pool. Thus for this particular design, the selection of the reactor fluid is a critical factor that should be taken into consideration.
Based on previous studies, the reactor fluid should have characteristics such as miscibility with effluents from the system, high heat capacity, and low hazard rating (Leung & Greenfield, 2006). In most batch polymerization reactors, water is thought to be suitability because of its non-flammability and miscibility with major monomers. With time, however, the fluid ha to be altered because water has a low freezing point. Alternative fluids that can be used are such as propylene glycol.
Problem Statement
The task is to seek whether most of the hazardous risks in chemical processes are due to some factors that can be incorporated in the design of batch polymerization reactors. Some of the optimal operating conditions, including the size of the fire ring for the batch polymerization reactor, type of solvents, accessibility, and containment design for the heat exchange system. To reduce the risks or hazards, polymerization batch reactors have to consider these factors.
Sizing
The first factor is sizing which will be on balancing the heat between the quench tank and the entire batch reactor. To get the correct sizing a number of considerations will have to be made. These include the complete boil-off of the solvent due to flammability, the initial temperature of the heat exchange system to be slightly above the room temperature, approximately 30 degrees, and complete reaction due to full adiabatic temperatures in the batch reactor (Leung & Greenfield, 2006). For the second case the process of runaway reactions will be completely dependent on time and only the vapor will be used to determine the containment design of the batch reactor. Therefore calculations for this will be based on the duration taken by the reactor to complete a batch of polymeric products which is roughly two hours. The intention of the design is to emphasize that small fire rings provide better mixing in the batch polymerization reactors and are not susceptible risks such as high pressure and flammability because of their ability to ensure that they do not corrode the quench tank.
Viscosity Characteristics
When designing containment batches for polymerization reactors, it is also important to consider the viscous characteristics of the flashing discharge. The viscous flow should below. Failure to which there will be a large carryover of materials in the process of relieving the batch reactor. Sequentially, a high viscous flashing discharge fluid will lower the relieving rate and increases the pressure which is potentially hazardous (Ni et al, 2016).
Thermal Stability
Another factor that has to be taken into consideration is the thermal stability of materials used in the design of batch reactors. It is important that the thermal stability to be counterchecked to ensure that it does not react with chemicals used for the polymeric processes.
Assessment of Safety
In most cases that hazardous conditions arise, usually the problem is linked to failure to assess the containment in polymerization reactors. Therefore another factor that should be incorporated in the design is how to assess safety. The best way to go about assessing the safety of batch polymerization reactors is by ensuring that even under the most severe conditions, it is having a safety index (Schork, 2017). A containment design is considered safe if the operator of the batch reactor has access to contents that are above the upper limits on the monometer as well as the initiator solution.
It is also worth noting that most chemical reactions are exothermic in nature and require the removal of heat. Therefore the accumulated heat must be controlled and the cooling steps followed in order to minimize the production of low-quality polymeric products or result in catastrophic events (Leung & Greenfield, 2016). One of the ways in which design can be improved for safety purposes is automating the heating and controlling system. Most of the batch reactors are standard types. However, even with automatic and computerized safety assessment techniques, the process has to be full-proof control to avoid the occurrence of catastrophic events. Designs should be such that they close all the loops that might compromise integrity operations.
In conclusion, most cases of hazardous conditions in chemical reactions arise as a result of the failure of thermal containment. The problem can be resolved by having designs that do not compromise the quality of the polymeric products but also maintaining thermal conditions. Based on the recent findings factors to be taken into consideration range from the type of coolant for the heat exchange systems, size of fire rings, and type of materials. Materials matter because of their miscibility with the solvent and the ability to have high temperature which is critical for the polymerization batch reactors.
References
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Hreiz, R., Latifi, M. A., & Roche, N. (2015). Optimal design and operation of activated sludge processes: State-of-the-art. Chemical Engineering Journal , 281 , 900-920.
Leung, J., & Greenfield, W. (2006). Containment system design. Process safety progress , 25 (4), 280-289.
Ni, L., Mebarki, A., Jiang, J., Zhang, M., Pensee, V., & Dou, Z. (2016). Thermal risk in batch reactors: Theoretical framework for runaway and accident. Journal of loss prevention in the process industries , 43 , 75-82.
Schork, J. (2017). Control of polymerization reactors . Routledge.
