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 :
- 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.
- 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.
- 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.
- 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. :-
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.
- 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.
- 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.
- 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.
- 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
- 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.
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 :-
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.
- 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.
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.
Back to Nitroglycerine Section page ~ Forward to Final Wash Hills
Forwards to Charge House, Block House and Acid Tanks
© 2006 Richard Edkins, Dalbeattie Internet.