Cracking idea – more from less

In this report we cover Responsible Care, a voluntary global initiative to improve the chemical industry’s performance, and progress of OPC – software that opens up specialist process industry software. Here, Anthony Gould explains how debottlenecking can

Capital investment by the chemicals industry in Western Europe has been in the doldrums for five years, and is not expected to rise significantly as the focus shifts further abroad – especially to the Far East. Finding low cost capacity enhancements at existing sites, however, is still very much on the agenda.

At the cracker end of petrochemicals, where complex hydrocarbons are split into less complex ones, there is much activity in unbottling ethylene production at existing plants, especially in the US and Europe.

World demand for ethylene is expected to grow 4.8% annually from 70 million tonnes to 111 million tonnes by 2005. In Western Europe alone six million tonne/year of additional capacity will be needed to meet the forecast increase in demand to 25 million tonne/year by 1015.

The main derivative of ethylene, polyethylene, which is used in the production of film, sheet, bottles, caps and pipes, is also on the rise by about 4% – driven in the main by demand from emerging countries.

Polyethylene’s share in ethylene demand is expected to rise from 56% now to 60% in 2005. Capacity in Western Europe is expected to increase from 17.5million tonne/year to 21million tonne/year by 2005.

Activity is spread across Europe. Shell Chemicals Europe is considering spending DM250m to expand capacity at its 650,000 tonne/year ethylene and propylene cracker at Moerdijk, the Netherlands, by up to 40%. The additional capacity would come on stream by 2000.

The projected 40% rise in capacity of the vapour cracker would be achieved at less than half the cost of a new plant. The project would involve installation of US-engineering giant Stone and Webster’s Advanced Recovery System technology.

Germany’s BASF has plans to modernise its Steamcracker 1 at Ludwigshafen, Germany, at a cost of DM100m and expand its annual capacity of 160,000 tonnes to 210,000 of ethylene by next year.

This will be achieved through modernisation, improved use of existing plant parts and of additional furnace capacity for the thermolysis of naphtha feedstock. Steamcracker 1, which uses steam at about 850xC to break down naphtha, will be fitted with a process control system.

ICI and BP’s Wilton cracker is also being overhauled. The project will increase the annual ethylene capacity from around 830,000 tonnes to 865,000. The £7.3m expansion will involve the redesign of compressors and installation of modern heat exchangers. Detailed design work was by Stone and Webster.

BP Chemicals intends increasing annual ethylene capacity at its two Grangemouth crackers to one million tonnes by 2000 from 700,000 today, with potential for 1.2 million tonnes. It will debottleneck its original ethylene cracker G4, brought on line 30 years ago, and its most recent cracker built five years ago.

G4 has a 270,000 tonne annual capacity. The project, expected to be complete by the end of 1998, should add an increment of 50,000 tonnes.

Capacity of the second cracker at Grangemouth will be increased from 440,000 to 710,000 tonnes annually.

Malcolm Hulatt, BP Chemicals engineering and project support manager, says debottlenecking has many attractions: it allows for an increase in capacity at relatively low cost, with the same number of employees – giving a reduction in the fixed costs/tonne.

An advantage over new build is that the extra product generated is not hard to find a market for whereas for new build you have to find a market for a large increase in capacity from day one, he says.

Debottlenecking – unlocking extra capacity by replacing or modifying elements of a plant which are constraining production – is traditionally achieved through a combination of more efficient furnaces and improvements to downstream equipment, such as optimising distillation columns or adding new ones.

It can also be achieved by analysis of existing equipment, enabling better performance to be squeezed out or the adoption of new catalyst technology which can produce radical capacity improvements.

On the BP’s older Grangemouth cracker, new furnaces will operate under higher severity cracking conditions. On the new cracker the greatest benefit will again come from installing Stone and Webster’s Advanced Recovery System technology which Hulatt describes as a `cost effective way of debottlenecking the refrigeration systems’.

The project will be assigned to a single business venture manager who will act as a single point of accountability. He will pull together everyone and everything involved in the project, from assessing the right tonnages, preparing the case and choosing and getting the necessary technology on board. BP moved to this system a few years ago. Previously it based projects on a matrix management system which could mean confusion over accountability.

BP has also changed the way it works with contractors by adopting integrated teams. BP and contractor staff work to achieve the same objectives and the same goal.

How long a plant needs to be offline for such an overhaul depends on several factors, particularly the amount of physical space available. Space permitting, the new equipment can be built alongside the existing equipment and switched over in a very short time.

An example of the second approach to debottlenecking can be seen at BP Chemicals’ polyethylene plant, also at Grangemouth, which was debottlenecked up to about 175,000 tonne/year from 100,000 tonne/year during the late 1980s.

BP’s engineers spent considerable time understanding the potential of the installed equipment to see how far it can be pushed beyond its original limits, at reasonable cost. `For example,’ says Hulatt, `if you understand the torque limit on a dryer or extruder, it may be possible to speed up the gearbox to run at a faster speed but at the same torque: or it may be possible to rewind a motor to increase its speed; or even replace the motor within its existing frame using the existing cabling.’

Since this project was completed the plant has had an old reactor recommissioned to produce 280,000 tonnes annually by the addition of a new compressor on one line and replacement of machines on another.

Each debottlenecking project is looked at a from a cost per tonne viewpoint. As a rule of thumb BP Chemicals would hope to spend less than 50% of the cost of new build.

The debottlenecking process can be seen as a number of possible stages. By plotting on a graph what increments in capacity different actions will provide at what cost, it is possible to see which actions should be taken in relation to market requirements. It may mean a phase by phase debottlenecking or one major project bringing them all together simultaneously.

New technology – process enhancements and improvements – is another driving force. New technologies are continually being developed which improve yields, save energy, simplify processes, improve catalysts or use alternative feedstocks.

BP Chemicals has launched three commercial technologies in the past two years covering polyethylene (Innovene technology), acetic acid (Cativa technology) and acrylonitrile.

BP’s polyethylene plant at Lavera in the South of France, originally built to an annual capacity of 130,000 tonnes, and which now produces 200,000 tonnes, will be debottlenecked further with the use of Innovene technology, a gas phase polyethylene process. BP has been working with Dow Chemical to combine Innovene technology with Dow’s Insite catalyst.

Cativa is a new iridium-based catalyst system, developed by BP’s engineering centre in Hull, to be incorporated into the methanol carbonhylation process, introduced by Monsanto in the 1970s, and which accounts for almost 60% of world acetic production. Acetic acid is used in the manufacture of the precursor for polyester fibre and resin for plastic bottles. BP claims that Cativa technology, which can be retrofitted, can reduce production costs by 30%.

The new catalyst is said to be more active than traditional rhodium-based systems, produces fewer by-products such as propionic acid and has lower energy requirements. The technology has already been tested at Sterling Chemicals, Texas City. BP plans to retrofit it to its A4 acetic acid plant in Hull and to install it at Ulsan in Korea. At Hull, the capacity of the 310,000 tonne/year plant will increase by one third next year.