Report by Christopher Hogarth
Manager Caltex Kurnell Refineries
In an ideal world, for every 100 barrels of feed to an oil refinery there would be 100 barrels of useful products made and there would be no other impact upon the community.
In reality, things are different. Not every barrel of feed ends up as a barrel of product. Some of the less valuable products are consumed to provide the energy required in the refining process. These products generally make up the refinery fuel gas pool, but in some cases can be fuel oil.
While some refineries do provide some energy to external facilities in various forms, they are all net consumers of energy. This means that either within the refinery or when looking at the greater picture, there is waste produced in association with the generation and consumption of that energy.
Refineries also employ catalysts and other chemicals. In the refining process, these catalysts and chemicals become 'spent' and therefore must be disposed of in an environmentally acceptable and hopefully economic manner. Waste is also generated in other forms such as flaring, sludge which can build up in storage tanks, and effluent water.
The energy that refineries take in or export is usually in the form of electricity, natural gas, steam or heat. Electricity can be purchased from the grid or produced within the refinery.
Modem refineries sometimes have co-generation facilities in which they can very efficiently meet their own electricity and steam requirements as well as exporting both. In Australia, natural gas and therefore energy is relatively cheap by world standards, and so Australian refineries are generally not as energy-efficient as their overseas counterparts.
However, energy is still far and away the biggest single component of a refinery's operating costs and so there is still a considerable drive for energy efficiency within Australian refineries. Refineries generally exhaust low-grade (ie low temperature) heat into their surroundings in flue gases and cooling water. In some Scandinavian countries where ambient temperatures are low and energy costs high, even this heat is recovered for space heating of houses and factories.
NEW TREATMENTS FOR SPENT CHEMICALS
There are various types of catalysts used in refineries, each having different properties and therefore different disposal options. Spent Fluid Cracking Catalyst (FCC) is generated continuously, typically at a rate of 2 tonnes/day. It has a talcum powder-like consistency.
It is heated to approximately 7000C in the presence of air to bum the
coke off in its final stage in the process, and therefore has no further
oil associated with it which can provide calorific value. It has been traditionally
disposed of as landfill, but is commonly now incorporated into concrete.
Spent reforming catalyst is produced in batches not continuously, typically every five years. Unlike FCC, it contains precious metals such as platinum and is therefore returned to the catalyst manufacturer for precious metal recovery.
Hydrotreating catalysts are also produced in batches but do not contain precious metals. They are usually sold to fertiliser manufacturers as a source of trace elements.
Spent polymerisation catalyst consists of phosphoric acid on a clay base, which is contaminated with long chain hydrocarbons. Unfortunately, within Australia to date, there has been no further refinement of treating options beyond neutralisation or immobilisation followed by landfilling.
Sulphuric acid of approximately 98% purity is used within certain refineries. When 'spent' its purity is reduced to between 92% and 93% and it contains acid-soluble oils. The acid is returned to the manufacturer where it is heated in a furnace to decompose it.
The decomposition products are then combined with other feedstocks for manufacture of the 98% pure product. Advantage is taken of the calorific content of the acid-soluble oils in the decomposition process.
Caustic soda is also used in various parts of the refinery process. The spent caustic has traditionally produced disposal problems for refineries. Caltex is currently finalising the commissioning of its new $15 million biotreater at Kurnell and has just successfully commenced feeding the spent caustic to it. The caustic is very beneficial in controlling the pH in the bioreactor.
REDUCED NEED FOR GAS FLARING
Refineries produce hydrogen, methane, ethane, propane, propylene and butane as off-gas. Historically, these have all ended up in the refinery fuel gas pool where, at best, they are burnt for calorific value in furnaces and boilers.
if, at any time, the fuel gas produced exceeds the demand of the boilers and heaters for fuel gas, the excess must be directed to the flare, which extracts no value from it.
In recent years there has been considerable effort put into finding alternative uses for these various components of fuel gas and thus eliminating, or at least reducing, the amount flared.
Hydrogen is now very valuable in refineries for removal of sulphur from refinery products, and as sulphur specifications get more stringent, refineries will need more and more hydrogen.
Propylene is a very valuable feedstock for polypropylene manufacture. The rapidly developing autogas business -in which propane/butane mixtures fuel transport vehicles such as taxis and hire cars as well as other heating applications for propane and butane - has resulted in considerable,effort now being directed at maximising recovery of both.
While the recovery of hydrogen, propane and butane discussed above has resulted in a significant reduction in refinery flaring, other measures have also been introduced. It is common for refineries such as Caltex's Kurnell refinery in Sydney to have flare gas compressors to recover flare gas.
Advanced techniques have also been developed for monitoring the condition of pressure safety valves (PSVs) to reduce the amount of hydrocarbon inadvertently being released into the flare system.
As mentioned, hydrogen is used to remove sulphur from refinery products. In this process, hydrogen sulphide is produced, which is partially oxidised to sulphur dioxide. These two products react to produce elemental sulphur. This process not only results in significant environmental benefits by reducing the sulphur dioxide and trioxide emitted to the atmosphere, it is also generates heat which is used for steam production thus reducing the amount that must be produced in the refinery's boilers. The elemental sulphur is used in fertiliser manufacture.
LESS SLUDGE, CLEANED-UP WATER
Sludge produced in refinery tanks was usually land-fanned, but it is now commonly consumed in power plants as supplementary fuel. The amount generated within a refinery is very small in relation to the amount of oil processed, and there are now technologies being used to further reduce sludge production and thus ensure that oil, which would
have previously have ended up as sludge, is now converted into valuable products. These technologies include the use of emulsion breakers as well as sophisticated tank mixing devices. All water that could potentially be contaminated with oil in a refinery is treated for oil removal before disposal. This usually includes primary separation techniques such as plate separators and induced air flotation units where the oil is separated and then fed back into the process to be recovered as valuable product. The water can then be treated in a biological reactor, as is the case in the new biotreater at Kurnell.
These examples show that significant advances have been made in oil refineries over the years to maximise recovery of valuable products and minimise waste production. In its 116,000 bpd refinery at Kurnell, Caltex prides itself in taking a very proactive role in this process.