Design Brief
(PROCESS SECTION 1):- Chlorine gas and liquid benzene are continuously fed to two parallel CSTR units (both operating at 60oC) with a molar ratio of 0.4 (mols Cl2/C6H6) i.e. the feed compositions for both reactor units are identical. All of the chlorine is consumed within the CSTR units producing both monochlorobenzene (MCB) and di-chlorobenzene (DCB) products. The DCB product from each reactor consists of the ortho (o-DCB) and para (p-DCB) isomers in an equimolar ratio. Hydrogen Chloride gas is produced as a side product in both CSTRs. The mass flowrate of the liquid product from CSTR_1 is double the liquid output from CSTR_2. The molar composition of both reactor liquid product streams is the same. The liquid stream outputs from CSTR_1 and CSTR_2 are mixed in a vessel before being pumped downstream. The composition of the liquid outflow from the mixing vessel is: Benzene (0.63 mf), MCB (0.34 mf) with the remainder consisting of DCB isomers. Unreacted benzene and chlorinated liquids are separated in a distillation column, K1, (you do not need to consider the detailed design of this column). K1 provides both a stream of highest purity benzene and a mixture of chlorinated hydrocarbons. High purity MCB product is subsequently output from a second distillation column, K2. You may assume that the DCB product stream contains no MCB. The DCB stream is cooled to 60oC and is then passed to a crystallizer wherein the temperature of the feed is reduced to 35oC and solid crystals of product are recovered.
5% of the benzene recovered immediately downstream from the CSTR section is recycled to the upstream CSTR feed line (here, recycled benzene is mixed with fresh benzene feed before being split and sent to the two CSTR units), the remaining benzene is used as a feedstock for a second chlorination process (SECTION 2) which is described below.?(PROCESS SECTION 2):- A second processing section uses recovered benzene and all hydrogen chloride gas from the upstream CSTRs. These materials are mixed with air and combined with a recycled distillate supplied from further downstream. Air is supplied such that oxygen is 50% in excess on a mol basis (that required by stoichiometry relative to benzene). The reactor is a fixed bed catalytic reactor operating isothermally at 320oC. Conditions are such that conversion of benzene is 40% (on a once through basis). There are no side reactions (you may assume that only MCB is formed and benzene does not combust in the reactor). You may assume that the process pressures are close to 1 bar (760 mmHg) absolute.
The fixed bed reactor output passes to a heat exchanger where condensable products are recovered at 50oC and gases (at the same temperature) are removed from the process. The recovered liquid is sent to a separator where the aqueous phase is removed. The organic liquid then passes to a shell and tube heat exchanger which raises the temperature of the stream to the bubble point temperature before being fed to a third distillation column, K3. The column top product (TP) distillate contains 5 mol% chlorobenzene. Part of this stream forms the recycled distillate mentioned earlier, the recycle ratio is 2.
The entire process facility, which runs continuously, must yield 300 kmol/day of mono- chlorobenzene. Process water is available at 10 °C and ambient temperature is 20°C. All columns operate with an external reboiler and total condenser.
Note: The brief contains several simplified scenarios and assumptions.
Main Tasks (this is not a comprehensive list, it is a shorter overview, consult the document 'Report Guidance' for further information)
1. Produce a process flow diagram of the process.
2. Perform a material balance for the production plant.
3. Design distillation column (K3).
4. Perform an energy balance for several items within the process.
5. Produce a design report.
Guidance -
This guidance is provided to aid you with the main aspects of the design. There are many other tasks involved in this process design, you should not consider this guidance as a complete check list. The scope of your design is dictated by you.
1. Flow diagrams
Produce a block flow diagram of the process indicating main units and the chemical species present in the process streams. Thereafter, produce a flow diagram which details all of the equipment and flow streams in the process. Your flowsheet can be refined as the project progresses, however the fundamental layout is likely to remain fixed. A key aspect of the project is the material balance, before you can undertake the material balance you must clearly identify where material enters and leaves the process. The final flowsheet will require a professional format, for this purpose, VISIO flowsheeting software is available however you may use other drawing software if you so wish. Your PFDs should assist with identification of chemical species, temperature and cooling/heating streams. You do not need to include pipe specifications. Consider that the PFD is the primary point of reference in your report and should therefore be produced to the highest standard.
2. Material Balances
The material balance is a key aspect of the project. To achieve your objectives you are required to use EXCEL spreadsheets, do not use modeling software (e.g. UNISIM) to generate your primary solutions. The Excel spreadsheet will calculate your material inventory in all of your process streams. You should select a basis for your calculations and identify relationships which describe the production, consumption and transport of material throughout the process. You may initially have to make some basic assumptions about certain stream compositions, these assumptions may be refined as the design evolves. Keep backup copies of your progress and save your work as a new file at select intervals, in doing so you have a fall back position in the event of a wrong turn in the calculations or work is lost etc. Consider producing a list of design variables e.g. recycle ratio, conversion per pass etc. which can be linked to the calculations within your balance tables.
3. Distillation Columns
The distillation columns are major components within the process. You may assume that the column feeds are at the bubble point. Assessment of the column's operating characteristics and verification of the composition of the top and bottom products is required. This will be achieved through the construction of the Vapour-Liquid-Equilibrium (VLE) diagram using Excel and modeling the effects of the operating lines you specify. You are required to determine the number of plates within your column and select a suitable reflux ratio. Do not use any other software to complete this task.
4. Energy Balances
Determine the specific enthalpies of components at input and output points from appropriate parts of the process and individual units (see report guidance). Use these values in conjunction with the material balances to determine the various stream enthalpies. Energy efficiency is extremely important in process engineering, consider ways in which you can make efficient use of your energy resources. You are required to report the energy characteristics of 5 process operations, i.e. calculation of the duty involved with all reactor control systems, energy balance calculations for the heat exchanger immediately downstream of the fixed bed reactor, the overall energy balance on column K3 and an analysis of the energy requirements of the crystalliser.
5. Design Report
Your design report will detail all aspects of the design process, for further guidance on the report format, additional content and emphasis you should refer to the document 'Report Guidance'.
Attachment:- Assignment Files.rar