Solvent reduction has been a problem for many industrial sectors since the introduction of Part I of the Environmental Protection Act around 1992. Nowhere have these issues been greater than for wood coating processes operated by furniture manufacturers.

Any wood coating operation using more than five tonnes of organic solvent in any 12-month period, should be authorised under process guidance note PG6/33. This requires all authorised sites to have implemented some common sense measures such as maintaining a solvent inventory, optimising transfer efficiency and minimising thinner use.

The legislation also requires companies to choose a ‘final compliance option’. In theory, there are three such options, but the vast majority of sites must opt for the ‘mass balance approach’. This states that large solvent users (more than 15 tonnes) should be applying no more solvent than solids by weight – ie a ratio of 1:1 or better. Smaller solvent users have until 2007 to achieve the more relaxed requirement of not applying more than 1.6 times as much solvent as solids, ie 1.6:1.

It has long been known that companies were struggling to meet these targets, but the problem had not been properly quantified. Likewise, it was not known how much companies had spent to achieve progress.

Solvent benchmarking

To address these issues, BFM Environment Ltd has completed a one-year study sponsored by Biffaward, a multi- million pound environment fund which uses landfill tax credits donated by Biffa Waste Services. The study concentrated up three sub-sectors:

Reproduction manufacturers: companies producing high quality furniture, with labour intensive coating involving many stages and ending with hand finishing.

Solid timber users: middle to top end manufacturers with fewer coating layers/operations and no hand finishing. This sub-sector includes companies that use real wood veneer on board material.

Board material users: lower to middle end manufacturers, often with three or fewer stages in coating processes, no hand finishing and a greater degree of automation.

Audits were conducted on 41 wood coating operations representing 10% of the UK’s wood coating solvent use and 20% of the UK’s authorised wood coating processes.

When comparing coating operations, the ratio of solvent to solids is one of the most useful performance indicators. Wood coating operations are designed to transfer solids onto timber. The amount of solids required over a given period will reflect the level of production: the greater the throughput of work the larger the total of solids.

Each tonne of solids requires an amount of solvent to achieve this transfer. Therefore, the ratio of solvent to solids is one measure that is already adjusted to take account of variations in production levels.

Although these ratios were far from compliant, they were significantly better than the performance in 1998 and a large amount of time and resource had been invested in solvent reduction.

Thinning solvents

The single most cost-effective solvent reduction method that virtually all companies had addressed concerned thinner usage. Cleaning thinners had been minimised through the use of lids on tins, cleaning procedures and the collection, reuse and recycling of dirty thinners. Thinning solvents had also been targeted and many companies with high solids coatings were using in-line heaters to reduce coating viscosity.

A sizeable amount of time and effort had been invested in coating reformulation.

Most companies had switched from traditional pre-catalysed sealers and lacquers to acid-catalysed and water-borne alternatives. However, the reproduction manufacturers were experiencing problems with this changeover – hence half of the companies retained some pre-catalysed coatings. As might be expected, ultra-violet cured coatings were in greatest evidence with board material users. But, one solid timber user had recently installed a small line for flat panels which would previously have been hand coated in three dimensional form.

All three sub-sectors were starting from a similar point in 1998 – having average solvent to solids ratios ranging from 3.04 to 3.58:1. Over two years, those using board materials progressed the most with a 48% drop in relative solvent use. Reproduction manufacturers made least progress with a 15% improvement.

Between 1998 and 2000, the 41 companies had reduced their solvent consumption from 1,475 to 870 tonnes – a saving of 41% or 605 tonnes per year. During this period, solids use decreased by just 8% from 468 to 430 tonnes. The relative stability of this solids figure shows that the solvent reduction was the result of proactive management rather than a simple decrease in production levels.

The cost of progress

Audited companies had spent a significant amount on upgrading between 1995 and 2000. Total capital expenditure among the 33 companies which gave information was £4.81m. This money was spent on items such as automatic application lines, spray equipment, drying tunnels and booths.

A further £565,000 was spent each year on solvent reduction consumables such as labour and material for trials and the additional cost of low solvent coatings.

Thus, total expenditure over five years was £7.63m – an average of £231,000 per company. The majo-rity of this cost was offset by annual savings of £1.46m associated with reductions in labour and coating costs following the implementation of changes. These savings totalled £7.3m over the five years – making the solvent reduction initiatives almost cost neutral.

However, it should be noted that the costs were highly sub-sector specific. The board sector experienced the highest capital costs of £280,000, but these led to annual savings of £73,000 – providing a payback period of around four years.

The reproduction sector fared worst, with capital expenditure averaging £77,000 per company compounded by annual costs of £26,000 – giving no payback for the upgrades.

Solvent waste

Audited companies consigned 136,400 litres of solvent waste off-site each year – which equates roughly with 98.5 tonnes of solvent. A further 36,600 litres of thinners (26.4 tonnes of solvent) were recycled on site.

The cost of solvent waste disposal averaged 28p per litre, though this varied greatly from 10-67p per litre. Some, but by no means all, of this difference can be explained by the volumes involved – suggesting that manufacturers should shop-around for quotations.

Twenty per cent of sites had a solvent recovery machine. These recovered 36,600 litres per year, leading to savings on virgin thinner purchases of around £47,580 and £10,248 on disposal costs. Most companies were using recovery machines with a 25 litre capacity. The average cost was around £4,500 with payback periods typically one year or less.

The full project report estimates that the sector emitted 10,500 tonnes of solvent in 2000 – a lower figure than that suggested by some other sources. A further 1,000 tonnes of solvent were sent off-site for reuse and recovery. But it demonstrated that significant differences exist between the three sub-sectors in terms of the degree of solvent reduction that can be achieved and the amount that must be spent.

Simplistic approach

These findings demonstrate the overly simplistic approach of the wood coating guidance note – trying to set the same target for processes which have little in common. A much more logical approach would be to recognise the differences in the nature of the processes and have different sets of ratios to reflect the levels of solvent reduction that are actually achievable.

It is also worth noting that there is little if any scientific justification for the 1:1 and 1.6:1 ratios. These were arrived at by European officials considering a wide range of industrial sectors, rather than anyone with a knowledge of the furniture sector. This would help to explain why only 29% of large solvent users had achieved compliance some two years after their deadline had passed.