Integrated parts(requirements) of a Chemical Process plant(safety,production specification,Environmental regulations,operational constraints,Economics)

A chemical plant is an arrangement of processing units (reactors, heat exchangers, pumps, distillation columns, absorbers, evaporators, tanks, etc.), integrated with each other in a systematic and rational manner. The plant's overall objective is to convert certain raw materials (input feedstock) into desired products using available sources of energy, in the most economic,way.

During its operation, a chemical plant must satisfy several requirements imposed by its designers and the general technical, economic and social conditions in the presence of ever-changing external influences (disturbances).

Among such requirements are the following:

Safety: The safe operation of a chemical process is a primary requirement, for the well being of the people in the plant and its continued contribution to the economic development. Thus, the operating pressures, temperatures, concentration of chemicals, etc. should always be within allowable limits. For example, if a reactor has been designed to operate at a pressure up to 100 psig, we should have a control system that will maintain the pressure below to avoid the development of plant.

Production specifications: The plant should produce the desired amounts and quality of the final products. For example, we may require the production of  two million pounds of ethylene per day, of 99.5% purity, from an ethylene plant. Therefore, a control system is needed to ensure that the production level (2 million pounds per day) and the purity specifications (99.5% ethylene) are satisfied.

Environmental regulations: Various federal and state laws may specify that the temperatures, concentrations of chemicals and flowrates of the effluents from a plant be within certain limits. Such regulations for example exist on the amounts of SO2 that a plant can eject to the atmosphere, and the quality of water returned to a river or a lake.

Operational constraints: The various types of equipments used in a chemical plant have constraints inherent to their operation. Such constraints should be satisfied throughout the operation of a plant. For example, pumps must maintain a certain net positive suction head; tanks should not overflow or go dry; distillation columns should not be flooded: the temperature in a catalytic reactor should not exceed an upper limit since the catalyst will be destroyed. Control systems are needed to satisfy all these operational constraints.

Economics: The operation of a plant must conform with the market conditions, i.e. the availability of raw materials and the demand of the final products. Furthermore, it should be as economic as possible in its utilization of raw materials, energy, capital and human labor. Thus, it is required that the operating conditions are controlled at given optimum levels of minimum operating cost, or maximum profit; etc