Hafiwo Consulting Group is looking for independent contractors to submit a bid for a client within the Ammonia industry. The client is looking for a design of a novel ammonia production plant that produces low carbon ammonia. Hafiwo Consulting Group has requested an analysis of your suggested plant wide process, safety risks and further manufacturing requirements associated with such a proposal. You have been shortlisted to develop a proposal to persuade Hafiwo Consulting Group you should be selected to complete the work.

DESIGN SPECIFICATION

The feedstock is an unlimited supply of hydrogen and nitrogen at specified temperature and pressure (see below for individual specification)

The plant should produce XX tonnes/day of ammonia at a purity of YY% (see below for individual specifications).

It is likely the design will require compression/expansion of feedstock, heating/cooling, a reactor, product condenser and separator, as well as a reactor recycle. But the specific design is up to you!

The design should produce a plant that has high efficiency and low emissions

The following values can be used to assess the economic feasibility of your process. For the purge stream, it is assumed that this is burnt, and so an economic value is given according to the methane and hydrogen contents, as given in the table above. The remaining components, argon, nitrogen, and ammonia do not burn and so do not give any value. The economic profitability should be calculated from: value of ammonia product, together with valuation of purge stream, less; cost of feedstock and utility costs.

Economic values used in the process (stream and value given below):

Nitrogen feedstock = $110/tonne

Hydrogen feedstock = $250/tonne

Ammonia product = $850/tonne

Cooling water = $2.7810-8/kJ

Power = $0.12/kWh

Purge hydrogen content = $210/tonne

Purge methane content = $310/tonne

Specification of feedstock conditions and required product rates and purity:

T (H₂) = 28 C

p (H₂) = 10 bar

T (N₂) = 18 C

p (N₂) = 6 bar

NH₃ rate = 1180 ton/day

NH₃ purity = 98.8 w%

You have been asked to develop a Process Flow Diagram, including simplified mass balances, for Ammonia production. Hafiwo Consulting Group would like you to:

Design, simulate and optimise a simplified ammonia production plant that produces low carbon ammonia

Develop a process description to accompany a corresponding Process Flow Diagram (PFD) that you simulated on Aspen Hysys

Use a simulation tool of your choice (e.g. Matlab or Excel or paper based calculation) to provide a comparison on a process wide mass balance with your simulation stream results, including a degree of freedom analysis. (You might need to relax some constraints, if you feel you need to then use your sound engineering judgement and dont forget to justify any assumptions made)

Using the simulation model, show the effect of changing the Purge flow and discuss your results. Change the purge flow in the range from 1% to 10% of recycle flow, and draw graphs showing:

a) The total molar purge flow

b) The ammonia product purity

c) Recycle flow

d) Recycle compressor energy