Chemical and Process Engineering

Home

Services

Clients & End Customers

Technologies

Case Studies

Contact JBL

Nanjing LDPE Project

Low Density Polyethylene

Client: Simon-Carves

2003/4

Senior Process Engineer

Project Background

SembCorp Simon-Carves Limited in co-operation with CTCI Corporation of Taiwan were awarded a contract by BASF-YPC (Yangzi Petro-chemical Company) for the design, supply and construction of a LDPE (Low Density Poly Ethylene) plant in Nanjing, Peoples Republic of China. This is the largest LDPE plant to be built in China, with a total capacity of 400,000 tonnes per year. It forms part of an integrated petro-chemical site.

Summary of Process

Click here for a simplified diagram of the process.

The process (from Basell Polyolefines GmbH) is based on a high pressure tubular reactor. Ethylene, produced at the adjacent petro-chemical complex, is supplied to the plant and compressed using hyper-compressors to a pressure of around 3000 bar.

The compressed Ethylene gas is preheated and passed through a number of tubular reactors into which organic peroxides are injected to initiate the reaction. The reactors are double pipe units with pressurised hot water flowing in the annuli. The polymerisation reaction is highly exothermal and the energy removed from the reaction is converted in to steam at various pressures for use within the LDPE plant and elsewhere on complex. Excess unused ethylene is separated after the reactors and recycled to the reactor feed system. The polymer melt is mixed with additives in an extruder to yield the final product. Some ethylene is carried forward through the extruder and the pellets are degassed with air during intermediate storage prior to being sent to final product storage. The plant comprises two independent lines, both of which can produce a variety of polyethylene grades. One line can produce both homo-polymer and EVA co-polymer whilst the other can only produce the homo-polymer. Polymer properties are controlled by the initiator, pressure, temperature profile and co-monomer content.

Specific Responsibilities

Instrument Data Sheets Mass Balance reviews

This large project required the preparation of data sheets for over 2000 instruments. I was responsible for a significant proportion of these. During their preparation checks were made as appropriate against the heat and mass balances (for up to 4 operating conditions), P&IDs, Licensor instrument data sheets, equipment data sheets, pipeline specifications and battery limit conditions. The instruments includes flow, level, temperature and pressure. I performed any necessary calculations to ensure correct specification of these instruments. During my contract in 2003 I was also responsible for dealing with control valve queries raised by the instrument department. This required checking data and performing pressure drop and line sizing calculations for incompressible and compressible fluids. The compressible fluids that I dealt with included Steam up to 40 barg, Nitrogen up to 300 barg and Ethylene to over 3000 barg. As well as calculation of pressure drops, thermal considerations associated with large changes in pressure were also necessary.

Process areas that I covered included:

Polymerisation reactors Peroxide preparation and dosing Degassing silos Low and Medium Pressure Hot water systems (including steam generation from these circuits)

I was re-engaged on the project in 2004 to assist with a range of residual process engineering issues. These included:

Assessment of Client's (CTCI) comments on "issued for construction" P&IDs. Investigation into additional instrumented over & under-pressure protection of degassing silos connected to the off-site regenerative thermal oxidiser. Hydraulic oil distribution system (including calculation of laminar flow pressure drops). Calculation checking.

Achievements

Experience working on a large petro-chemical project. Identification of anomalies. Processing of a large number of data sheets.

Documents Produced Instrument data sheets for pressure, temperature, flow and level transmitters. Data sheets for pressure regulators. Calculations in support of instrument and pressure regulator specifications. Calculations for pressure drop, line sizing and control valve size checks. Specialist Software "InTools" for creating process specifications for instrumentation. "PDMS Reality Review" for 3D plant layout visualisation. "TASC5" for shell and tube heat exchanger design.

Hazards Considered Pressures up to 3100 Barg Process temperatures down to minus 50 C Explosive gases and vapours Problems Identified and Solved Bottle-neck in nitrogen purge system. Extreme low temperature caused by expansion of bottled Nitrogen used for purging. Over-specification of flowmeters and hence saving in large bore pipework and fittings. Frost protection requirements. (minus 14 C ambient). Liaison Other Engineers; Process, Control, Mechanical, Piping.