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Ministry of Supply Factory, Dalbeattie -
 View of Nitration Hills, Unit 2 (Edingham)

Ministry of Supply Factory, Dalbeattie
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Nitroglycerine Sectiion -
Nitration Houses [Code AB]
:-

Key Points :-

  • Nitration of glycerine using concentrated nitric and sulphuric acids.
  • Two-storey Nitration House inside Hill.
  • Schmid continuous nitration process.
  • Separator unit and three wash columns.
  • 'Drowning Tank' on lower floor.
  • Ancillary tanks for compressed air and waste (refuse) acids.
  • Elaborate control measures to stop explosions.
  • All buildings demolished during decommissioning, but most of the hills remain.

Ministry of Supply Factory, Dalbeattie - Interior of Nitration Hill, Unit 2 (Edingham)
Interior of Nitration Hill - Schmid Nitrator Mounting with Separator plinth (hidden by Elder tree). Fume tower base on top of hill bank.


Nitroglycerine Nitration Houses at the M/S Factory Dalbeattie :

The Nitration Houses were the highest of several embanked Houses at each NG Hill. The function of the earth bank and brick was to contain and direct upwards any accidental explosion. A two-storey structure, the Nitration House was designed with a large water tank under it and various tanks, whilst the main procesases took place on the upper floor. The following section summarises a rather complex process from the firsthand description of Mr. Gordon Nicholson, Acid Plant Manager at M/S Factory Dalbeattie during 1941 to 1943.

RAF air photographs from 1941 - 1946 confirmed that the AB Houses were in pairs linked by a footbridge, with a heavy wall and pier midway to prevent blast travelling from one AB House to the other. Both AB Houses survive in Unit 1, but only one of them in Unit 2. This has meant considerable re-evaluation of the NG Hills and functions.

The code 'AB' for these Houses apparently refers to Nitration (A) and Separation (B) processes. This is why there is not a separate 'B' House.

Nitration House Top Floor :

  1. The Displacement Tank : Located beside and above the Nitrator and Separator, this stainless steel tank held 'Synthetic Refuse Acid', a weaker mix of the strong acids used to charge those two units before a nitration run and to displace the reacting acids and nitroglycerine at the end of a run. It was filled from the 'Acid Egg' on the ground floor level of the Hill by compressed air displacement.
  2. The Schmid Nitrator : Mixed acid and glycerine were reacted in a small steel chamber about 39 inches (1 metre) high and 28 inches (70 cm) internal diameter, with a chilled brine cooling jacket and an internal mechanical stirrer. Thermometers fitted to the Nitrator allowed the operator to check that the mix was not becoming either too hot or too cold, as overheating could result in nitric oxide fume production and the risk of spontaneous detonation of the nitroglycerine. The reactor could hold 8.1 cubic feet of the mixture being reacted, amounting to about 890 lbs of acid. Reaction was continuous, with nitroglycerine rising to the top of the Schmid reactor and overflowing through pipes into the adjacent separator.
  3. The Primary Separator : The acid and nitroglycerine mixture overflowing from the Nitrator flowed down a stainless steel tube to an inlet in the base of the Separator. This resembled a rectangular steel box 161.5 cm x 85 cm x 85 cm, inclined at 45° to the horizontal, with 35 corrugated plates inside it, slightly shorter than the length of the box. The acid and nitroglycerine gradually separated, the lighter nitroglycerine rising to a draw-off pipe, which was opened once sufficient nitroglycerine had accumulated. The capacity of the Separator was about 51 cubic feet, or about 5600 lbs of acids. This allowed a much slower flow than in the Nitrator, allowing the nitroglycerine to accumulate. The refuse acid (R/A) was drawn off at a lower level, initially being stored in a tank at the lower level of the Nitration Hill, then when this 'acid egg' was full, the excess spent or refuse acid (R/A) was diluted slightly with water and sent to tanks outside the hill.
  4. The Wash Columns and Intermediate Separators : Three columns 8 feet high were located in the Nitration House. Each consisted of glass cylinders stacked on top of one another, with stainless steel perforated diffuser-plates and rubber glands joining them. The assembly was held together by aluminium bands around the joints and vertical rubber-covered steel rods, linking the cast-iron base plate to the stainless steel head, which had a fume vent to the top of the building. Impure Nitroglycerine from the separator was piped with injected cold water to the base of the first column, which was filled with water at at least 12° C. and was aerated with low pressure air. The nitroglycerin/water emulsion spilled over into a small tank of warm water - the intermediate separator. Nitroglycerine being heavier than water, the nitroglycerine sank and the wash water flowed from the top of the intermediate separator, the nitroglycerine then flowing to the bottom of the second wash column, where the process was repeated in water at 40% C. The third wash-column used 1.3% sodium carbonate solution to slowly neutralise any remaining acid over some 12-15 minutes, before discharge down a rubber pipe to the second Wash Hill. Flow rates were not rapid either for the nitroglycerine or the water, which were in fed into each tower in almost equal proportions, so wash water consumption was kept to a minimum.

Nitration House Ground Floor :

On the lower floor of the Nitration House or alongside it within the protective embankment, were the following structures. :-

  1. The Drowning Tank : The main reason for a two-floor nitration house was safety. Underneath the house process level was a 2,000 gallon tank of cold water. If temperature in either the centre of the Schmid Nitrator or the Separator head exceeded 28° C, or a thermometer in the side of the Separator exceeded 30° C, thermostats operated to break the power to electromagnets on valves in the base of both Nitrator and Separator, so the overheated mixture was immediately discharged and doused by the water in the drowning tank, which automatically is aerated and topped up with more water. Alternatively, the discharge cocks can be opened by a lever in a blockhouse set outside the embankment, or by a switch that cuts off all power. A similar arrangement allowed operations staff in the Nitration House to use a lever or a pull-switch to drown the reacting mix within about 40 seconds.
  2. Air Storage Tank : High pressure air at 75 lbs/square inch (2.5 atmospheres) from a 930 cubic feet storage vessel beside the charge house, was reduced to about 28 lbs/square inch (0.9 atmospheres) low pressure air before being piped into a 100 cubic feet vessel in the ground floor of the Nitration House. This low-pressure air was used to drive the mixed acid, glycerine and wash-water solutions to where they were needed, and where necessary to aerate the mix.
  3. Refuse Acid Tank ('Acid Egg') : This tank was used during start-up and shut-down, when a quantity of 'Synthetic Refuse Acid' was used to flush out and fill the Nitrator and Separator with a clean solution of weak acids uncontaminated by Nitroglycerine.
  4. Refuse Acid / Spent Acid Tanks : These lead-lined tanks took in the slightly impure and diluted refuse acid from the Separator during a nitration run. They were periodically emptied and the refuse acid pumped to the Acid Plant for treatment and recycling.
  5. Soda Wash Barrel and Cascade : Two minor but important elements used to collect and neutralise start of run and end of run acid and Nitroglycerine from Separator flushings and then to separate it by slow flow and settlement across a cascade of small tanks or channels on an inclined plate. The recovered Nitroglycerin was put in the first intermediate separator of the wash columns.
Thanks to Malcolm Bowditch and Les Hayward, whose 'Pictorial History of RNCF Holton Heath' is worth 15, the writer has acess to illustrations of an earlier and smaller version of the Schmid equipment. The wash towers on that unit are under 5 feet high, but give an idea of the equipment used.

1931 Schmid Nitrator at RNCF Holton Heath
1931 Schmid Nitrator at RNCF Holton Heath
1931 Nitroglycerine Separator at RNCF Holton Heath
1931 Primary Separator at RNCF Holton Heath
1931 Wash Columns and Intermediate
 Separators at RNCF Holton Heath
1931 Wash Columns and Intermediate Separators at RNCF Holton Heath

Archaeological Remains of the Nitration House :

The Hill consists of a rectangular brick encloser surrounded by an oval bank with a slope of about 45 degrees, with one entry tunnel at first floor level facing the tank supports, a second below ground level under the first floor entry, with signs of pipe supports, a third entry tunnel at about mid-floor level, again with pipe supports, and a wider ground level entry tunnel coming out near the presumed Wash Column support plinth. The first floor entry tunnel is lined with acid resistant gritless asphalt, as is the 'bridge' leading from it towards the (missing) Nitration House. From the 'bridge' level there are three visible concrete structures :-

  • A large concrete vertical pillar with metal strapping on its face at first floor level. This is presumed to be the support of the Schmid Nitrator and its Displacement Tank.
  • Two reinforced concrete support columns to First Floor level. This may be the support for the first floor and part of the substructure for the Primary Separator, which would have would have weighed several tonnes when full.
  • A lower-level concrete block with two rows of heavy bolt studs set into its top - 3 on one side, 6 on the other. This would match the hold-down studs required for the three Wash Columns and their Intermediate Separators.
Below there is the concrete edging for the Nitration House which may have been a frame structure clad with asbestos cement panels. Because of overgrowth, the floor of the Unit 1 Nitration House is hidden by turf and the Unit 2 sNitration House is much the same. It is likely that careful surface excavation will be needed to obtain further detail.

Nitration House interior showing
 Nitrator support, Separator supports and Wash Column plinth
Unit 2 Nitration House AB1 interior showing Nitrator support, Separator supports and Wash Column plinth
Unit 1 Nitration House AB1 : Wash Column plinth, Separator support, Upper and lower access tunnels
Unit 1 Nitration House AB1 : Wash Column plinth, Separator support, Upper and lower access tunnels
Unit 1 Link bridge and blast wall between AB1 and 2
Unit 1 Link bridge and blast wall between AB1 and 2 Nitration Houses
Unit 2 was similar.

Conclusion :

This account and these pictures of the continuous nitration process at Dalbeattie may be the only ones currently available on the Internet. The writer acknowledges the assistance of Gordon Nicholson's family in making this information available.

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© 2006 Richard Edkins, Dalbeattie Internet.