This is a part two of the Advance Process design project. Part one was a group project in which we carried out a feasibility study of Methanol to Olefin (MTO) plant. The plant is an extension of an existing Coal-chemical complex in China, which produces 1,000,000 tonnes of methanol from coal each year. In order to become more competitive in the market, we studied alternative routes of MTO process and designed the most efficient, least pollutant and safest plant. The aim of this individual project is to cover a detailed design of the C2 splitter distillation column which is the final step in the MTO process where ethylene and ethane are separated. As ethylene is one of the most popular petrochemical product and the demand for the product is continuously increasing each year. Therefore, to meet the customers demand the column was designed with 99.4% purity.
For the initial design calculation, the operating pressure of the column was chosen as 24bar. The diameter of the column was calculated to be around 1.66m for the stripping section, which was suitable for the sieve plate design. Using the AlChE method, the plate overall efficiency was obtained as 73%, which was in the range of the distillation column efficiencies, by using the plate efficiency the actual number of stages was obtained, 53 stages, with an overall height of the column as 35m. At 24bar the condenser duty of the column was calculated to be 2.66MW and reboiler duty 2.43MW. The design optimisation shows that as the pressure of the column increases, the capital cost of the column also increases due to the increase in a number of actual stages and the reflux ratio, mean taller and thicker column wall, will be required to meet the right specification and to handle the high pressure of the column. But, with the increasing pressure, the energy cost of the column decreases, as less energy will be required to condense the overhead vapour. The capital cost of the column outweighs the energy cost of the column. Therefore, the column total cost increases with the increase in column pressure. The optimum pressure, for the C2 splitter column, was chosen as 10bar. The reason being, low reflux ratio and less number of stages will be required, meaning the less capital cost of the column.
Table of Contents
1.0 Project Brief
2 Project Objective
2.1 Technical Objectives:
2.2 Personal Objectives
3 Introduction
3.1 Theory
3.2 Process Description
4 Chemical Engineering Design
4.1 Mass Balance
4.2 General Design Considerations
4.3 Bubble point for the Condenser and Reboiler
4.4 Minimum Number of Stages (Fenske Equation)
4.4:1 Minimum Reflux Ratio
4.5 Gilliland Correlation
4.6 Feed-Point Location
4.7 Internal Traffic
4.8 Energy Balance
4.8:1 Condenser Duty
4.8:2 Reboiler Duty
4.9 Physical Properties of the Mixture
4.9:1 Vapour density
4.9:2 Liquid density
4.10 Estimation of column diameter (Dc)
4.10:1 Calculating Flooding velocity
4.10:2 Estimation of Downcomer area (Ad)
4.10:3 Column diameter in the Enriching section Dc:
4.10:4 Column diameter in the Stripping section Dc:
4.10:5 Summary of Calculations
4.11 Provisional Plate Design
4.11:1 Types of tray
4.11: 2 Plate design Procedure
4.11: 3 Plate construction
4.12 Plate Efficiency – AlChE method
4.12:1 Gas-Phase Mass Transfer Units NG
4.12:2 Liquid phase transfers unit NL
4.12:3 Vapour Liquid Equilibrium diagram for HK and LK Component.
4.12:4 Point Efficiency can be calculated using the following equation:
4.12:5 Overall Column Efficiency
4.12:6 Actual Number of Plates
4.13 Column Height
4.14 Feed-Point Location
4.15 Design Optimisation
4.16 Evaluation
5.0 Mechanical Design
5.1 The Material of Construction
5.2 Design temperature
5.3 Design Pressure
5.4 Maximum Allowable Stress
5.5 The Welded – Joint Efficiency
5.6 Corrosion Allowance
5.7 Thickness of the wall under internal pressure
5.8 Heads
5.8;1 Flat Head
5.8;2 Hemispherical Heads
5.8:3 Ellipsoidal Heads
5.8:4 Torispherical Heads
5.9 Loading analysis
5.9:1 Dead weight
5.9:2 Wind Loading
5.9:3 Stresses Analysis
5.9:4 Check for Elastic stability or Buckling
5.10 Vessel Supports
5.10:1 Skirt Supports
5.10:2 Skirt support design
5.11 Tensile check
5.12 Manhole size
5.13 Estimation of Pipe diameter
5.13:1 Feed pipe diameter
5.13:2 Distillate Pipe Diameter
5.13:3 Reflux Pipe Diameter
5.13:4 Bottom Pipe Diameter
5.13:5 Vapour reboiler Pipe Diameter
5.13:6 Enriching section Pipe Diameter
5.14 Concept Drawing
6.0 Data Sheet
7.0 Control and Instrumentation P&ID
7.1 The objectives for the control system of the C04 distillation column are.
7.1:1 Temperature/ Composition Control for distillate and Bottom
7.1:2 Pressure control for the distillation column
7.1:3 Level control in the column and reflux drum
7.1:4 Liquid level in the bottom of the column
7.1:5 Quality Control
7.2 Alarms, Safety Trips and Interlocks
7.2:1 Primary objectives
7.3 Instruments
7.3:1 Pressure instrument
8.0 Piping & Instrument Diagram
8.1 Tag Sheet
9.0 Economic appraisal
9.1 Capital cost
9.1:1 Bridgewater Method
9.1:2 Zevnik and Buchanan
9.1:3 Amortisation
9.2 Raw materials
9.3 Income
9.4 Operating Costs
9.4:1 Energy Costs
9.4:2 Labour
9.4:3 Insurance, Maintenance, Tax and Royalties
9.4:4 Total Fixed Capital Cost
9.5 Operation at 600,000 t/y
9.6 The Breakeven analysis
9.8 Operation at 1000000t/y
9.9 Return on Investment (ROI)
9.10 DCFrr
9.11 Cash flow for 600,000 t/y
9.12 Cash flow for 1,000,000 t/y
9.13 Optimisation
Project Objectives and Key Topics
The primary objective of this project is to conduct a detailed chemical and mechanical design of a C2 splitter distillation column, which serves as the final step in a Methanol-to-Olefin (MTO) process to separate ethylene from ethane with high purity. The study involves mass and energy balance calculations, column sizing, material selection, mechanical integrity analysis, and the development of a comprehensive control and instrumentation scheme to ensure safe and efficient operation.
- Detailed chemical engineering design and mass/energy balancing of a C2 splitter column.
- Mechanical design, including wall thickness calculations and structural support analysis.
- Process control strategy development, including P&ID generation and safety instrumented systems.
- Design optimization to balance capital expenditure against operational energy costs.
- Economic evaluation to determine process feasibility and breakeven production rates.
Excerpt from the Book
4.2 General Design Considerations
Low-pressure C2 splitter – with refrigeration/heat pump
Low-pressure C2- Splitter is a preferred technology for ethylene/ethane separation. It uses a heat pump to condense the overhead vapour. In the heat pump or refrigeration system, the vapour leaving the column is compressed, condensed in the reboiler and partially refluxed back to the column.(7) Advantages – Process uses low temperature, high relative volatility mean easy separation and short time of thermal exposure. Disadvantages – Power consumption of refrigeration or heat pump cycle is around 0.65MW(5) and this system also results in very high vapour velocities, which can cause flooding in the column. (6)
High-pressure C2 splitter
C2 splitter columns are normally operated at high pressure, as the overhead vapour is condensed in a more conventional manner due to increasing in condenser temperature, but more stages are required for separation. [7] Advantages – The system is less complicated as it may not require refrigeration compressor or heat pump. Enthalpy of vapourisation decreases with the increase in pressure, therefore, lower condenser and reboiler duty.[7] Disadvantages – The relative volatility decrease with the increase of column pressure, more reflux or stages are required to perform the separation making it high cost and high energy incentive process. The wall thickness of the column increases to handle the high pressure. The diameter of the column decreases due to the fact that vapour in the column will have higher density (High-pressure drop in the column). [7]
Summary of Chapters
1.0 Project Brief: Provides an overview of the MTO project scope, including plant extension goals and the focus on the C2 splitter column design.
2 Project Objective: Outlines the technical and personal goals set for the completion of the project, including design tasks and professional development.
3 Introduction: Discusses the underlying theory of distillation and provides a detailed process description of the C2 splitter setup.
4 Chemical Engineering Design: Details the mass and energy balances, determination of stage numbers, column dimensions, and overall plate efficiency using the AlChE method.
5.0 Mechanical Design: Covers material selection, wall thickness, head design, and structural analysis including loading and vessel support calculations.
6.0 Data Sheet: Summarizes the final design specifications and operational data for the C2 splitter distillation column.
7.0 Control and Instrumentation P&ID: Explains the control objectives, instrumentation strategies, and safety systems implemented for efficient plant operation.
8.0 Piping & Instrument Diagram: Presents the final engineering diagrams for the piping and instrument layout.
9.0 Economic appraisal: Evaluates the capital costs, operational expenses, and overall economic feasibility of the plant at different production rates.
10.0 Conclusion: Reviews the project objectives and summarizes the final design choices and operational recommendations.
Keywords
Methanol-to-Olefin, MTO, C2 splitter, distillation column, ethylene, ethane, process design, mass balance, energy balance, sieve plates, mechanical design, process control, P&ID, economic evaluation, chemical engineering.
Frequently Asked Questions
What is the primary purpose of this research project?
The project focuses on the detailed design and process engineering of a C2 splitter distillation column, which is essential for separating ethylene and ethane in a Methanol-to-Olefin (MTO) chemical plant.
What are the core thematic areas covered in this report?
The report covers chemical engineering calculations (mass/energy balance), mechanical design (vessel integrity), process control instrumentation (P&ID), and economic assessment of plant feasibility.
What is the main objective of the C2 splitter design?
The primary goal is to achieve 99.4% purity for ethylene production, ensuring the process is safe, efficient, and cost-effective under specified operating conditions.
Which scientific methodology is utilized for the design process?
The project utilizes the AlChE method for plate efficiency calculations, the Fenske and Gilliland correlations for determining stage requirements, and standard mechanical design codes for column integrity.
What topics are explored in the main body of the document?
The main body treats the mass/energy balances, calculation of column diameter and height, design of sieve trays, selection of construction materials like mild carbon steel, and a comprehensive economic evaluation.
Which keywords best characterize this work?
The work is characterized by terms such as MTO process, C2 splitter, distillation design, sieve plates, ethylene purification, and process economic appraisal.
Why was 10 bar selected as the optimum operating pressure for the column?
Optimization studies indicated that 10 bar provides an ideal balance by requiring a lower reflux ratio and fewer stages compared to higher pressures, which significantly reduces the total capital cost of the column.
How is the safety of the column managed in this design?
Safety is managed through an integrated control and instrumentation system, featuring alarms, automatic trip systems for pressure and level control, and HAZOP studies to identify and mitigate potential failure points.
- Quote paper
- Sharyar Ahmed (Author), 2016, Production of a Plant Making 600,000 t/y Methanol-to-Olefin (MTO), Munich, GRIN Verlag, https://www.grin.com/document/903164
