How to do chemical process design?

3.4 Supplementary Notes

Chemical technology majors still need to participate in the preliminary work, the main preliminary work is:

Project proposal; Preparation of feasibility report.

Project quotation; Preparation of tender and technical documents.

Introduction project: including inquiry, tender evaluation, contract technical annex negotiation.

Overall planning and design of large and medium-sized combined installations.

4 Process design method

4.1 Selection of process route

Factors to be considered: raw material source, economic and social benefits (production costs), environmental protection, other operating conditions, safety, fire protection, investment, technological advancement, feasibility and rationality opinions.

4.2 Optimization of process plan

▲ Optimization of reaction process

There are many and complicated problems to be considered in the optimization of reaction process. Such as reaction kinetics, reaction yield, catalyst characteristics, reaction course, reaction path.

The optimal operating conditions of the reactor include how to ensure the reaction temperature, reaction pressure, mixing requirements, heat transfer requirements, the ratio of each material, and the production cost under given conditions.

▲ Optimization of rectification process

If the distillation process needs to separate R components, R-1 rectification column is required.

Rectification optimization needs to consider: which component is the main product, which component is the product and the product specification requirements.

Distillation process optimization method 1) : trial method, the main rules are as follows:

Normal rectification is preferred.

Try to avoid decompression operations and use of cooling capacity.

The number of products should be minimal.

Corrosive and dangerous components should be separated first.

The components that are difficult to separate are finally separated.

The largest number of components shall be separated first.

The top of the tower and the products of the tower reactor are best separated by equal moles.

Optimization method of rectification process 2) : optimization method

Distillation process optimization method 3) : mathematical programming method

▲ Optimization of evaporation process

Single effect, double effect, triple effect evaporation.

Heat pump evaporation, membrane evaporation.

Multi-stage flash evaporation.

Forced circulation evaporation, natural circulation evaporation,.

The selection is based on the type of evaporator (standard, suspension frame, Levin, forced circulation evaporator).

4.3 Selection of process equipment

▲ Reactor

The choice of reactor should be based on material properties, stability, reaction complexity, product scale, reaction time, temperature, pressure and other factors

▲ gas-liquid mass transfer equipment

1) Plate tower: bubble cap, float valve, screen plate, etc. The flow direction distribution type of plate tray can be divided into U-shaped flow, single overflow, double overflow and so on

2) Packing tower:

Lacey ring, ball ring, moment saddle ring and other packing.

Loose, structured packing.

Solid packing, screen packing.

The selection of the above mass transfer equipment should be based on the separation difficulty, pressure drop size, vacuum (heat sensitive materials), material nature, investment situation, corrosion situation, material cleaning situation, safety requirements, elasticity size, foaming and other conditions.

▲ Heat transfer equipment

Divided by function: cooler, condenser, heater, heat exchanger, reboiler, steam generator, superheater, waste heat boiler, etc.

According to the structure type: The heat exchanger using two flow heat exchange is divided into the following five types from the structure

A. Shell type (fixed tube plate, floating head type, stuffing box type, U-shaped tube type)

B. Plate type (plate fin type, spiral plate, umbrella plate, corrugated plate)

C. Tube type (air cooler, tube type, spray pipe type, box type)

D. Liquid film type (lifting film type, scraper film type, centrifugal film type)

E. Other types (shell type, heat pipe type)

The selection of the above type of heat exchanger is based on:

A. Fixed tube-plate heat exchanger: fixed tube-plate heat exchanger that is, both ends of the tube plate and the shell are connected into one, because the shell process is not easy to repair and clean, so when choosing A fixed tube-plate heat exchanger, the shell fluid should be cleaner and not easy to scale the material; When the temperature difference between the two fluids is large (greater than 60℃), thermal compensation should be considered, and the temperature difference between the two fluids is not easy to be greater than 120℃.

B. Floating head heat exchanger: the heat exchanger shell is easy to clean, but the inner gasket is easy to leak, suitable for heat exchangers that need to compensate for thermal expansion, and the temperature difference between the two fluids is greater than 120℃.

C.u-type tube heat exchanger: "The heat exchanger is convenient to manufacture, install, low cost, pipe resistance to high pressure, but the structure is not compact." It is suitable for high temperature and high pressure situations, and the fluid in the tube must be clean.