I. PROBLEM STATEMENT

Synthetic ammonia $(N{H}_3)$ refers to ammonia that has been synthesised $($Standard Industrial Classification $2873)$ from natural gas. Natural gas molecules are reduced to carbon and hydrogen. The hydrogen is then purified and reacted with nitrogen to produce ammonia. Approximately $75$ percent of the ammonia produced is used as fertilizer, either directly as ammonia or indirectly after synthesis as urea, ammonium nitrate, and monoammonium or diammonium phosphates. The remainder is used as raw material in the manufacture of polymeric resins, explosives, nitric acid, and other products.

At Siyinqaba Petrochemicals where you are practicing as a Chemical Engineering Technologist, anhydrous ammonia is synthesised by reacting hydrogen with nitrogen at a molar ratio of $3$:$1,$ then compressing the gas and cooling it to $-33C.$ Nitrogen is obtained from air, while hydrogen is obtained from the catalytic steam reforming of natural gas, methane $(C{H}_4).$ Six process steps are required to produce synthetic ammonia using the catalytic steam reforming method: $(1)$ natural gas desulfurisation, $(2)$ catalytic steam reforming, $(3)$ carbon monoxide $(CO$ shift, $(4)$ carbon dioxide $(C{O}_2)$ removal using monoethanolamine solution as the absorbent$,(5)$ methanation, and $(6)$ ammonia synthesis. The first, third, fourth, and fifth steps remove impurities such as sulfur, $CO,C{O}_2$ and water $(H_{2}O)$ from the feedstock i$.$e$.,$ hydrogen, and synthesis gas streams. In the second step, hydrogen is manufactured, and nitrogen $($air$)$ is introduced into this two$-$stage process. The sixth step produces anhydrous ammonia from synthetic gas. While all ammonia plants use this basic process, details such as operating pressures, temperatures, and quantities of feedstock vary from plant to plant.

It has been reported that the $C{O}_2$ removal packed absorber is experiencing some difficulties in achieving the required exit gas composition of $1.A^{**}$mol$\%$ of $C{O}_2.$ After inspecting the packed column $($internal diameter of $1.B^{***}m),$ you have concluded that the current problem can be resolved by optimising the absorbent flow rate. Note that, at column current conditions, the $K-$value of $C{O}_2$ is $0\mathrm{.}8B^{**}$ and estimated values of $k_y$a and $k_x$a are $2A{B}^{***}mo\frac{l}{m^3}.hr$ and $1B{A}^{***}mo\frac{l}{m^3}.$ hr$,$ respectively. As such, you have been tasked to prepare a detailed report based on your preliminary findings about the $C{O}_2$ absorber$.$ Your report should include findings on the following:

a$)$ The minimum absorbent flow rate to operate the column aimed at achieving the required $C{O}_2$ composition in the exit gas stream,

b$)$ Sensitivity analysis calculations aimed at investigating the effect of absorbent flow rate on the packing height $($present a minimum of three cases$).$

c$)$ Indicate the best design option in terms of the absorbent flow rate, supported by a clear discussion.

d$)$ Justify values of selected variables, assumptions made, and the validity of the proposed design on the basis that specific operational problems are avoided, and purity requirements are met.

Your report will be surveyed by the Process Development Division and used as a basis for further decisions on the proposed project, as such any assumptions made must be clearly justified. Enclosed you will find essential information related to this project as well as guidelines on how to present your