Читать книгу Encyclopedia of Renewable Energy - James Speight G., James G. Speight - Страница 132

A batch process is usually performed over and over, and batch processes are a sub-class of sequential processes. Batch process refers to a process that involves a sequence of steps followed in a specific order. Also, batch processes generate a product but the sequential processes need not necessarily generate a product. Thus, batch processing is a technique for automating and processing multiple portions of a feedstock More generally, industrial processes can be divided into two categories of production which are (i) continuous processes and (ii) batch processes.

Continuous processes are designed to run at steady state, and to maximize the efficiency of these processes, it is necessary to keep the plant in the operating range under disturbances. The optimization task required to operate such processes is usually performed to achieve disturbance rejection, designing controllers to reach and maintain set-point effectively, and keeping the down time to a minimum. Since the operating range is generally very narrow, the system dynamics can often be approximated by linear dynamics.

Batch processes have a finite operating time, rather than a continuous operation. The control objective in batch processing is not to reach steady state, but to reach some desired objective by the end of the batch. This can involve movement through a very wide operating range, and non-linearity in the system can be strong. Batch optimization focuses on maximizing the performance objective by finding the corresponding input variable and state variable trajectories. Since batch production is usually of low volume, high value production, optimization of its operation is critical to make the process viable.

The most common type of process for acid gas removal is the batch-type process, and many involve a chemical process in which the acid gas reacts chemically with the cleaning agent, usually a metal oxide. These processes are not merely physical separation processes in which the acid gas is removed by a physical phenomenon, such as adsorption. Thus, the batch-type processes have the common requirement that the process be operated as a batch system where, at the end of the cycle, the chemical agent must be changed or regenerated in order to continue treating.

Batch processes are limited to removing small amounts of sulfur from fuels, especially when the flow rates of the gas streams and/or there are small concentrations of hydrogen sulfide. These processes include (i) the iron sponge process, (ii) the ChemSweet process, (iii) the SulphaCheck process, (iv) the SulphaTreat process, (v) the zinc oxide process, and (vi) the molecular sieve process.