Reference no: EM132160211

CASE STUDY - Production of Formaldehyde

PROBLEMS -

1.1. What is the world production rate of formaldehyde in kg/h?

1.2. Construct a detailed flowchart showing known compositions, flow rates, and temperatures. Use this chart to keep track of your calculations and as a basis for a final flowchart to be prepared when you have finished the case study.

1.3. Determine the feed rate of methanol to the process (kg/h), neglecting trace amounts of formaldehyde and methanol in the off-gas stream from the absorber.

1.4. What is the percentage conversion of methanol for the process?

1.5. At what rate is methanol recycled to the reactor?

1.6. Does the specified air flow rate produce a gas mixture with a composition outside the explosion limits?

1.7. What is the flow rate of air to the reactor in (a) kmol/h and (b) standard cubic meters/min?

1.8. At what temperature should the vaporizer operate?

1.9. Because of its high solubility, essentially no methanol leaves the absorber in the off-gas stream. Determine the flow rates of water and formaldehyde in this stream.

1.10. What is the feed rate of water to the absorber? By increasing the water flow, the size of the absorber could be decreased. Why, then, is it desirable to limit the water flow rate to this amount? (Hint: Consider the ultimate fate of the water fed to the absorber.)

1.11. If the liquid leaving the column were saturated, could it be made to absorb any more methanol and formaldehyde without first being cooled? Explain.

1.12. The liquid and vapor streams leaving the reboiler are in equilibrium. What is the temperature of each stream and the composition of the vapor stream?

1.13. Is it possible to determine directly from the presented equilibrium data the dew point of the gas leaving the reactor? Compare the dew-point temperature of this gas as calculated from Raoult's law with the observed value of  100°C. Does the solution behavior follow Raoult's law? Explain.

1.14. Examine the process flowchart and description carefully and itemize the utility consumption units (those that require steam, cooling water, and electricity).

1.15. Determine the minimum energy requirement of the blower in horsepower. How does your answer change if the blower is 40% efficient? (See note at the end of the list of questions.)

1.16. What is the purpose of the waste-heat boiler? Give reasons why, in practice, the reactor and waste heat boiler are combined in one unit.

1.17. What are the standard heats of Reactions 1.1, 1.2, and 1.3?

1.18. What is the rate at which steam is fed to the reactor? Determine the temperature of the reactor effluent stream if no steam were fed to the process. What role is played by the steam fed to the reactor?

1.19. What fraction of the hydrogen produced by Reaction 1.1 is consumed in Reaction 1.2? Would more or less steam be required if Reaction 1.2 proceeded to completion? Explain. What would be the required process changes if Reaction 1.2 were suppressed completely?

1.20. At what rate is steam generated in the waste-heat boiler?

1.21. Recognizing that increased residence time in a reactor usually means a higher conversion, why might the length of the reactor be only 3 cm? (Hint: Consider the possibility of unwanted side reactions.) What problems in heat transfer are presented by such a small reactor?

1.22. Assuming ambient air and stored methanol to be at 25^oC, how much heat must be supplied to the vaporizer? Assuming that a portion of the steam generated in the waste-heat boiler could be used for this purpose, estimate the required flow rate.

1.23. What is the required flow rate of cooling water to the exchanger between the waste-heat boiler and the absorber?

1.24. How much heat must be removed by the two heat exchangers cooling the recycled absorber liquid? Why is there a need to remove this heat?

1.25. The liquid entering the reboiler, the vapor entering the condenser, the liquid leaving the condenser, and the vapor and liquid from the reboiler may be considered saturated. How much heat must be added to the distillation column through the reboiler?

1.26. Can the available cooling water be used to condense the overhead stream from the distillation column? Explain.

Additional Problems for Study -

1.27. Estimate the total cost of raw materials and compare these with the current selling price of 37% formaldehyde solution.

1.28. Establish the source of commercial methanol. A useful reference is the Kirk-Othmer Encyclopedia of Chemical Technology.

1.29. Estimate the cost of utilities required to operate the process.

1.30. Suggest alternative arrangements for connecting energy-consuming operations with energy producing operations, with the objective of reducing the cost of operating the plant.

Note on Problem 1.15. The solution to this problem requires thermodynamics beyond the scope of this text. To calculate the minimum energy requirement, assume that the compression is adiabatic and reversible, and that C_p/C_v = 1.4.

Note - NEED ALL QUESTIONS ANSWERS AND DRAW FLOWCHARTS.

Attachment:- CASE STUDY - Production of Formaldehyde.rar