Structured reactors operational costs

As the previous ehapter discussed nuelear power reactor operation and how to perform a PSA on it, this chapter attempts to apply a similar framework to chemical processing. The problem is the diversity of chemical processing that blurs the focus. This chapter begins by showing that accidents in the chemical process industry cost lives and dollars. Descriptions of deadly chemical accidents arc presented to show the chain of sequences that were involved to suggest how their PSA may be structured. Background on selected hazardous chemical process is presented followed by descriptions of how their PSA have structured. The chapter concludes by applying FTAPSUIT to a pressure vessel rupture analysis. 

Catalytic processes are an essential operation of large-scale processes in the chemical industry. Appropriate micro structured reactors offer an increase in efficiency compared with conventional reactors if a method can be found to integrate low-cost devices in industrial practise. Automated procedures will enable professional manufacturing of reactors with an acceptable cost/performance ratio. 

With honeycombs (monoliths), pressure drop could be reduced by a factor of 100 or more, with corresponding reductions in equipment and operating costs. The total absence of radial flow in such structures, however, precludes their use in multitube reactors the bulk heat generated by the reaction would not be transported to the tube walls, the selectivity of the process would decrease dramatically, and prevention of reaction runaway would prove difficult. Furthermore, the lack of radial vectors means that inhomogeneities in radial velocity profiles would be maintained these inequalities in residence time would reduce selectivity and result in poor utilization of the catalyst in many of the channels. 

New reactor types for three-phase operation are still being developed. An example is the application of structured reactors, which may have certain advantages in three-phase operation, and can be operated with co-, cross- as well as with countercurrent flow. A very recent development is the use of monolith reactors (Fig. 8.9) in three-phase operations. Their advantages are the small pressure drop, the good external mass transfer, the short diffusion distance, and the low adiabatic temperature rise. Disadvantages are the higher catalyst costs, importance of liquid distribution, and moderate catalyst load. 

The structure of a slurry reactor is much simpler than that of a multitubular fixed-bed reactor and so it is about 45% cheaper to build. Since the slurry phase is an excellent heat exchange system, there is no need, as in the case of fixed-bed reactors, to recycle a large portion of the efffluent gas in order to obtain both a high conversion (fresh feed basis) and good temperature control. The operating cost of a slurry reactor is hence lower. If the objective is the production of high yields of FT waxes, then the slurry system appears to be a better proposition. The slurry system, however, would require an additional unit to separate the fine catalyst from the wax product. 

The key result of the Hierarchical Approach is the development of the basic flowsheet structure, formed by Reactor-Separations-Recycles. This structure defines the material balance envelope. In this respect of highest importance is the behaviour of the reaction system, which should deliver a realistic image of the reaction mixture. Other constraints regarding the reactor operation, as molar ratio of reactants, or safety requirements, are determinant for the structure of recycles. Optimal conversion represents a complex optimisation problem between the valorisation of raw materials and the cost of reactor, separators and recycles. 

In control structure scheme 4 fresh feed makeup F )a eontrols reactor level. Fresh feed makeup F )d controls the reactor composition zh Reactor effluent is flow controlled. This scheme works well. However, it requires an additional composition analyzer, This may be a serious drawback in many processes because of the high capital and operating costs of some analyzers and because of their poor reliability. 

Some components may be fabricated at the dedicated assembly facility others will be purchased from outside vendors. In addition to the reactor assembly, it is envisioned that the turbine generator and several building structures will constitute the major assemblies. The major assemblies will be delivered to the site as modules. Some components, materials, and services will be purchased locally. The site must be prepared, the modules installed and connected together. Operational costs will include the costs of operating the reactor system and the turbine/generator. Decommissioning costs have also been considered, but on a present value basis they are minimal. 

Novel Processing Schemes Various separators have been proposed to separate the hydrogen-rich fuel in the reformate for cell use or to remove harmful species. At present, the separators are expensive, brittle, require large pressure differential, and are attacked by some hydrocarbons. There is a need to develop thinner, lower pressure drop, low cost membranes that can withstand separation from their support structure under changing thermal loads. Plasma reactors offer independence of reaction chemistry and optimum operating conditions that can be maintained over a wide range of feed rates and H2 composition. These processors have no catalyst and are compact. However, they are preliminary and have only been tested at a laboratory scale. 

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