The Solvent Recovery Plant at Sun Printers, Watford

Norman Oldknow,
Heating and Ventilation and Recovery Engineer

I joined the Sun in 1956 at the start of the big expansion of the Gravure Department.

Pre-war, the major part of the gravure printing was done on German Vomag machines, which were much wider than the early 30” and 56” machines.

The introduction of the new high-speed Goss machines brought about the big changes in the main press hall. The roof was raised and the Goss and Vomag machines were laid out side-by-side. Over the roof a new system of extract ducts was installed to lead down to a tunnel under the railway line to the site of the new Recovery Plant.

The original plant was built pre-war by the CECA company of France and was operated manually. The new equipment was built by the English offshoot of the company and was British CECA. The design of the [new] plant was completely different and incorporated the latest control and detection methods which had been developed in the 1950s.

The main function of the plant was to draw the solvent vapour from the gravure presses, capture the molecules and recycle them to be used again. This diagram, originally published in Impressions, shows how the system worked.


In the gravure machines, the three basic colours and black were each applied to the paper web in separate printing units. This system demands that each colour has to be dried on the web before passing into the next unit, thereby building up the final four-colour picture. This drying process determined the overall speed of printing production.

The inks were dissolved in a very volatile mixture of petroleum distillate and toluene, which is related to the benzene family from the distillation of coal-tar. Every unit had a powerful fan which blew air through a heater battery into the drying hood where the warm air was forced through narrow slots to scour the paper and dry the ink. The extract fans above each press took away a portion of the drying air through filters into the main ducts over the roof.

At this stage, the main fans of the Recovery Plant on the south side of the railway line took over and fed the solvent vapour to the adsorbers. An adsorber takes another substance into its whole volume, as in the case of a jelly with its colour. In this case the adsorbers were large steel tanks which held tons of activated charcoal, which has the property of being able to trap the solvent molecules at the surface while the carrier air-stream is discharged to atmosphere. This is the same principle which was used in wartime gas-masks to purify the air.

When the charcoal was saturated with the solvent, a signal from a detector closed the main valves and a steaming period was operated, during which the solvent was liberated from the surface of the carbon and transported through water-cooled condensers. The liquid phase dropped into a settling tank, in which the water and solvent separated, as the two liquids are incompatible. At this stage the solvent overflowed to its storage tank and the condensed steam ran away to drain.

At the end of this cycle, the adsorber was re-opened to the air stream and the next unit in line was prepared for steaming.

The large quantity of cooling water needed for the condensers was provided by a separate cooling tower plant and storage pond. The accumulated solvent was pumped daily to Dr. Fuchs’ ink factory at Ascot Road.

When all the Gravure machines were working, the solvent recovered was equal to the load of a 5000-gallon petrol tanker being re-used each day, so it was a considerable blessing to the environment over West Watford, as well as being an important economic factor in the ink manufacture. Consider also that the same scale of environmental effect was being achieved at North Watford where the Odhams gravure plant was almost identical to the Sun unit.

Two major expansions of the plant followed as the gravure presses increased. Firstly, the bigger 90/91 machines were introduced with their wider web widths.. Then the Italian Cerutti machines were installed for the TV Times contract. The second great period of growth followed the Odhams-Sun merger, with the introduction of more presses and a major effort to provide another complete set of duct-work which carried the extracted air over the railway to new adsorbers built by Croftshaws of Colchester. At this point computer control was introduced, which could vary the main fan speeds according to the needs of the press room and [had] a more efficient method of steaming the vessels. The solvent plant was such a major user of steam that the boilerhouse also had to expand in line with all the changes in the press room.

Some technical details

As the solvent or “recovered spirit” was so flammable almost every mechanical piece of plant was operated by compressed air. All electric motors for pumps or fans were flameproof.

The concentration of vapour in the drying hoods at the press was most efficient at 10 grams / cubic metre of air. At higher levels than this, the ink on the paper web started to re-absorb the solvent and so impeded the drying.

All the air which was taken away by the exhaust system had to be replaced by the huge ventilation plant, which occupied the entire floor level over the wages office in the five-storey building. The air was filtered and supplied to the press room at the proper humidity and temperature for the machine minders and the paper web.

The importance of the working atmosphere had gradually become apparent as more research was done on toxicity levels in industry. International standards were applied for the safe levels of factory conditions. In the case of the solvents, the level was down to a few parts per million of air. This could be checked by an infra-red gas analyser, designed by the Grubb-Parsons Co. of Newcastle, and by Drager analysis tubes from Germany.

At one period in the early days, we had annual visits from the Customs Dept. to inspect our vessels and products because technically we were distilling our product. At another time we had to add a dye to the spirit, to deter any use as motor fuel.

Note: Mr Oldknow’s last sentence, “... we had to add a dye to the spirit, to deter any use as motor fuel” is relevant to a parallel cost-reduction effort in which senior management was involved at that time, remission of road tax ...

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Gravure Petroleum-based Diluents

C.R. Greenhill [written early 1964]

Gravure printers [in Britain] have always paid road tax on the petroleum-based diluents used in their inks (2/9d a gallon to November 1964, 3/3d a gallon thereafter). On a number of occasions campaigns have been initiated, through the Eastern Regional Board for Industry, to claim remission of this tax.

On February 25th 1963 the West Herts District Committee made a new approach, backing it with a statement of the cost of diluents used in the gravure industry (provided through the European Rotogravure Association). The Eastern Regional Board approved the case, and the NPACI obtained the support of the Midland Regional Board (Car Manufacturers and Coachbuilders) and the FBI [Federation of British Industry].

On September 4th 1963 at an Eastern Regional Board meeting, the treasury representative explained the difficulty of supplying petroleum-based derivatives at two prices, and the dangers of abuse of any of the concessions to industry. We proposed that these concessions should only be granted to companies who could prove the use by authentic recordings, and that the tax should first be paid for all spirit, and remission claimed on the recorded consumption.

The treasury have made arrangements which, while not exactly in line with our proposals, do in fact allow for the tax to be reclaimed from September 1st, 1964.

Eastern Regional Board, ref E/1/4, s II, para 4:

INDUSTRIAL OILS RELIEF – Relief from Hydo-carbon oil duty on light oils used as raw materials in industrial processes will be granted with effect from 1st September. This relief will be extended to heavy oils used as ingredients in the manufacture of other articles.”

This will have considerable effect on cost at Watford and, indeed, at Paulton [Purnells].

I do not have the exact figures for Watford, but I would imagine at least 450,000 gallons for 1964 and 500,000 gallons for 1965. The saving would be over £20,000 for the 4 months of 1964, i.e., 150,000 gallons @ 2/9d and for subsequent years £81,000, i.e., 500,000 gallons @ 3/3d.