Introduction to Process Design

☄️In the 2nd post, we will talk about generalized approaches to process design. Let's begin 🤩

GENERALIZED APPROACH TO THE CHEMICAL PLANT DESIGN

💡Design of chemical plant involves chemical technology, unit operations, instrumentation/controls, use of specialized equipment, safety considerations, materials of construction, etc.

🛠Chemical technology is the branch of chemical engineering dealing with chemical changes and physical methods involved in industrial process. It is necessary to supplement the knowledge of unit operations with considerations of chemical technology in order to obtain a concept of the complete plant. From the above discussions, it is clear that before attempting process engineering design it is necessary to fix the product specifications. Capacity of the plant can then be decided based on demand and/or investment. Evaluation of available technologies will have a say on investment. In order to arrive at consumption figures of raw materials and energy, preliminary stochiometric calculations would be necessary. This would give some rough idea of cost of production due to inputs which normally accounts for higher proportion in the cost. Following sequence might be followed in implementation of the project right from conception of the idea to construction and operation of the plant:

1. Process Research

2. Preliminary Process Design

3. Preliminary Process Evaluation

4. Process Development

5. Final Process Design

6. Final Process Evaluation

⏱Now, it is time to give brief information about all,

Process Research and Pilot Studies

🔌Process Research is the basic necessity and additionally, development of pilot plant is also necessity, particularly where laboratory scale data are not sufficient to scale up. Such pilot plants can result in eliminating production of off-spec product, good yields and reduced cost of manufacturing and etch. by fixing the best operating conditions 🤫. Pilot plant can be used for ongoing improvements of the existing process or development of a next generation process. One of the objectives of such a study is substitution of a raw material. Improvement in product quality, reduction in process costs, safety and minimizing the pollution effects are other objectives of the pilot study.

👻Lastly, a process flow diagram can be offered by a team leader for further process design based on pilot plant studies.

Process Design and Development

📌After carrying out process research and pilot plant study, the process details are now available to the process engineer which can be scaled up with sufficient confidence level to a commercial plant. Scale-up from a pilot plant to manufacturing scale plant cannot be simply carried out by geometric scaling. Use of dimensionless numbers is recommended in scale-up for process designs.

Now, going back to the 1️⃣st post, we had given the main responsibilities of process engineers. Here I will share in detailed way 🌝

The process engineer is not concerned with detailed design of pieces of equipment but is concerned with the overall process covering following major items:

1. Preparation of a block diagram for presentation to the management for preliminary feasibility of the project.

2. Carryout overall and individual material balances showing the yield and quality of all materials to and from all pieces of equipment.

3. Heat balances over each piece of equipment.

4. Prepare a Process Flow Diagram (PFD) based on data in Steps (2) and (3).

5. Establish flow quantities and suction and discharge conditions of all rotating equipment.

6. Size reactors and storage tanks.

7. Separation process calculations with optimum operating conditions to effect the desired separation.

8. Estimate utility requirements such as steam, cooling water, refrigeration, electricity, thermic fluid, fuel, etc.

9. Prepare a Piping and Instrumentation Diagram (P&ID) so that requirement of instrumentation/control system is assessed.

10. Develop a tentative layout of the plant that should take into considerations of safety requirements.

11. Estimate preliminary capital investment and production cost.

After completion of the preliminary process design and its evaluation, detailed process design work is taken up. For the detailed design, variety of tools’ are used in calculations. Estimation of properties by group contribution methods, literature search for different types of reactors, correlations for heat transfer, pressure drop and mass transfer calculations, mixing, etc., are the tools available to a process engineer.

Final Stage

On completion of all the above steps, final PFD and P&ID are prepared by the process engineer and handed over to the project manager with equipment datasheets (containing process specifications) for further execution of the project.

In this post, we have clarified what are the project stages and given detailed information about responsibilities of ours 😁!

Thanks for your time to read and Stay tuned! 😉✨

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