CAPE 2050- Group Design Project 2021-2022 Resit: Synthesis Gas Production

Process Description

Green Chem is a spin-off company with the drive to commercialize a new, direct process synthesis approach to producing synthesis gas directly from CO2 and H2. The process considers molar feedstocks as follows: CO2 available at 45oC and 5 bar with a composition of 99% CO2, and 1% H2O and H2 available at 60oC and 5 bar with a composition of 99% H2 and 1% CH4. H2 and CO2 are fed to the process in a molar ratio of 3:1. Both feedstocks are mixed with a compressed CO2 recycle stream at 5 bar. The mixed feed stream is preheated to 700 oC using a furnace and reacted over a nickel catalyst to produce synthesis gas. The hot reactor effluent is cooled to 40 oC and sent to a separator where 100% H2O is knocked out. The cooled, dry synthesis gas is sent to a membrane separator where CO2 is recovered, compressed, and recycled. The product stream leaves the membrane separator at 1 bar, and 40 oC.

Reaction Kinetics

CO2 and H2 react endothermically according to the reverse water gas shift (RWGS) reaction to produce CO and H2O over an adiabatic nickel-based reactor. The exothermic methanation side reaction also occurs, whereby CO and H2 react to produce CH4 and H2O. The per pass conversions for both RWGS and methanation reactions are 45% and 2% respectively, using CO2 and CO as the limiting reagents. The heat of reaction (ΔHr) at standard conditions (25oC) for both reactions are as follows:

RWGS= 41,000 kJ/kmol; Methanation = -210,000 kJ/kmol.

Pressure drop information

The pressure drops across furnaces and coolers can be assumed as 10 kPa for both shell and tube sides. The water separator operates at inlet cooled synthesis gas conditions (temperature and pressure). The reactor pressure drop is given as 200kPa. The CO2 (recycle) side of the membrane separator operates at 2.1 bar and 40 oC.

Individual Project Information

Students must use the brief as well as individual information (this will be emailed) such as feedstock molar flowrates, CO2 recovery factor and annual process operating time to develop the process flowsheet and answer the following questions (Sections A-D).

Section A- Mass balances

            Perform a mass balance over the process, ensuring mass is conserved. Also, estimate the extents of reaction for both RWGS and methanation, the total CO2 recycled and the annual synthesis gas production rate for the process.

Section B- Energy Balances

            Using the heat of reaction method, and enthalpy data from the Elementary Principles of Chemical Processes, estimate the outlet temperature of the adiabatic reactor.

            Draw a process flow diagram, giving equipment ID/names for process units, temperatures, and pressures where appropriate as well as total stream molar and mass flows and molar composition.

Section C- Heat Exchanger Design

Green chem is considering the installation of a boiler feed water (BFW)/synthesis gas cooler in its pilot plant application using copper tubes. TEMA proposes the following heat exchanger design (Table 1) for the unit operation:

Table 1

TEMA Fixed Shell- 4 tube pass Exchanger, Copper tubes, Counter-current Design

Shell Side/ Tube Side fluid assignment   Reactor Effluent Synthesis Gas/ BFW

Tube Outer Diameter    19 mm

Tube thickness  2 mm

Tube Arrangement        Triangular

Tube Straight length      1.8 m

Specific Heat Capacity of Synthesis gas   1.754 kJ/kgoC

Shell Side Inlet/Outlet Temperatures     159/69 oC

Tube Side Inlet/Outlet Temperatures     35/58 oC

Fouling factor Shell side/Tube side         5000 W/m2C

Thermal Conductivity of Copper 400 W/m2C

Shell side heat transfer coefficient, hs    984 W/m2C

            Using the mean specific heat capacity and mass flow data from Section A for the reactor effluent, estimate the duty for the exchanger in kW.

            Using the assigned temperatures given above, calculate the Ft correction factor, LMTD for the exchanger and the mass flow of BFW water required.

            Using an assumed overall heat transfer coefficient, U, estimate the heat transfer area and the number of tubes per pass required.

            Calculate the heat transfer coefficient for BFW using the equation below:

h_i=(4200(1.35+0.02T_m ) u_t^0.8)/(d_i^0.2 )

Where, hi = tube side heat transfer coefficient for water, W/m2C; Tm = mean BFW temperature, oC; ut = water velocity, m/s; di = tube inner diameter, mm.

            From your answer in part IV and the data given in Table 1, calculate the overall heat transfer coefficient, U, using the rigorous design criteria. An error estimate between the assumed and calculated U of <+15% would be deemed appropriate and justified.

            From your calculations in part V or otherwise, calculate the design heat transfer area for the exchanger.

Section D- Pump Design

The piping network for BFW system is given as follows:

BFW is available from a BFW tank, with a fill height of 2m from the ground at a pressure of 1 bar. The BFW pump skid sits 0.5 m from the ground. The total suction piping required is 0.5m and there is one globe valve at 100% open on the pump discharge. The distance from the pump to the BFW/synthesis gas cooler is 10m; the piping follows in an easterly direction for 5m and continues 5m in a northern direction at 90 degrees. The cooler sits on saddles with a tube side entrance height of 1.75m from the ground. The piping exits the tube side outlet of the cooler and continues to a height of 10m, where it enters the BFW/steam drum operating at 48 bar. The distance between the top of the exchanger and the entrance of the tube side of the cooler requires 0.2m of piping. The BFW/steam drum requires an additional 0.5m of piping to connect the outlet of the cooler to the inlet of the vessel. Green Chem considers schedule 40 commercial steel piping, with a velocity specification of 2 m/s and an absolute roughness of 0.046mm. Assume all bends are 90 degree sharp bends.

            Utilize the information above to produce an isometric sketch of the layout of the BFW piping segment.

            Estimate the tube side pressure drop of the exchanger, frictional pressure drop and deduce the pump pressure head. Note: You can neglect the viscosity correction factor when estimating the tube side pressure drop.

            Given that the efficiency of the pump is 55%, estimate the power required.

Report Structure

The submission for this assignment should be in the form of a written report, produced using Microsoft Word or any other text base program. The font should be Arial and the font size should be 11, with a spacing of 1.5 and limit of 15 pages. The report should entail an executive summary (500 words max), describing key results obtained as well as a general introduction linked to the process importance and overview. Furthermore, it should entail a title page with module code, student name, date of submission and project title (Synthesis Gas Production) as well as a body detailing the results of Sections A-D. Please make use of sample calculations where necessary, with complete equations and answers. Excel solutions, Tables of results as well as diagrams can be appended if necessary-however, they should be referenced in-text as to where the information can be found. Please remember to round values to 2 significant figures, use SI units throughout the report (pressures can be reported in bar, temperatures in oC, flows in kmol/h and kg/h), reference any data/properties etc., and account for assumptions where appropriate. The deadline for submission on Minerva is 15th August 2022 at 14:00 UK time. Individual project information will be emailed to each student.

Reference Material

Elementary Principles of Chemical Processes- Mass and Energy Balances, Enthalpy Data can be found in the appendices.

Chemical Engineering Design Volume 6- Coulson and Richardson 4th Edition (or any edition-note chapter numbers maybe different). Chapter 5- Piping and Instrumentation, Chapter 12- Heat Transfer Equipment.

Notes on pressure drops and pump design are given on Minerva.

Mark Scheme

1          Executive Summary

2          Mass Balance    10

3          Energy Balance 15

            Heat Exchanger Design

            Heat Duty

            Flow Rates

            LMTD, Assumed Area and U

            Tube Velocities, Tube Passes, Tube Length

            Inside HTC

            Overall HTC and Error Justification

            Design Heat Transfer Area

5          Isometric Sketch (with dimensions)        10

   b        Pressure Drop:

            In Heat Exchanger – tube-side + nozzles

            In piping, incl. bends, valves, etc 10

b          Specification of Pump:

            Head developed

Pump Power

9          Process flow diagram with equipment codes and stream data     6

10        General – Layout, English, References, Units, etc.           6