SAFETY AND ENVIRONMENTAL PROTECTION IN A SYSTEM OF

PRODUCTION, STORING AND DISTRIBUTION OF AMMQNIA

BY

Dr. Theo Huberich

of

BASF AKTIENGESELLSCHAFT

AMMQNIA.DEPARTMENT

D-6700 LUDWIGSHAFEN/GERMANY

Paper for the

Symposium on Safety in Ammonia Plantsand Related Fecilities

American Institute of Chemical Engineers

Montreal / Canada

October 1981

1. Outline of BASF's posi tlon

In its Ludwigshafen works BASF produces in three plants daily upto 2500 metric tons of ammonta, which has to be deliveredpartly in gaseous and partly in liquid form to numerousindividual users within the works area. Some of theconsumers require liquid airanonia not as a raw material forsynthesis but for cooling purposes and therefore return gaseousairanonia to the network. Delivery to subsidiaries andpurchase of supplementary airanonia is handled by tank barges,while smaller outside customers are supplied by railtank cars. Some customers also take aqueous airanonia sol utionby way of railway tank cars or tank trucks. Storage capacityhas been installed to compensate for production outages andfluctuations in demand.

2. Statement of the problem

For the distribution of ammonia an interlocking grid hasbeen instalied which has to fuifi 11 the following re-quirements:

- Reliable supply of liquid,gaseous and aqueousammonia to various consumers even in case ofproduction outages or breakdown of one plant.

- Adaptation of the supply ratio of liquid andgaseous ammonia to the demand, which fluctuatesparticularly according to the season..

- Guarantee of maximum safety

- Compliance with. environmental regulations

^' Description of the Supply Grid

For the distribution of liquid, gaseous and aqueous ammoniaa pi pel ine grid of a total length of 70 km (40 miles),

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including branches, has been insta "lied in the ludwigshafen works.

The liquid aranonia grid is direct! y connected to the production

plants. Spherical tanks for the storage of about 2000 metric

tons ammonia at ambient temperature (pressure approximately

10 bar [145 psij ) are available to equalize short-term

fluctuations in supply and demand. In order to keep the grid

pressure of 25 bar (363 psi) independent of the pressure in the

intermediate expansion vessels of the synthesis plants, a buffer

vessel with a volume of 100 m (3500 ft ) is incorporated in the

grid, into which gaseous ammonia is constantly fed at a temperature

of 60 °C (140 °F). The flow into and out of the pressure storage is

controlled according to the liquid leve! in this buffer vessel.

The actual storage to cover the demand for ammonia during shut-

down of the synthesis plants consists of two large pressure-

less tanks, each of which holds 25 000 metric (27560 shtn)

tons of ammonia. The pressure in these cold storage

tanks is maintained by means of screw compressors, which

draw off the gas that normaUy evaporates in the tanks and

transfer it into the gaseous ammonia grid. For feeding

pressurized ammonia into the cold storage tanks a refrigeration

unit with reciprocating compressors is available. Cold

ammonia is heated to at least 5 °C (40 °F) by heat exchange

with hot water before i t is introduced into the 25 bar (363 psi)

liquid ammonia grid. The cold and pressurized ammonia storage

are connected by pi pel ine to a loading doek in the harbor,

where refrigerated and pressurized tank barges can be loaded

and unloaded. Railway tank cars can receive or discharge

pressurized ammonia at a railway loading station.

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The grid for gaseous ammonia operates at a pressure of 2 bar abs

(28 psig). It receives gaseous ammonia from the refrigeration

units of the synthesis plants and from the users of liquid

ammonta for-eooling purposes.

The volume of ammonia gas made available by the synthesis plants

can be controlled by operating their refrigeration units with

or without their ammonia compressors. If a further matching

between supply and demand is necessary, a unit for pressurizing

and liquefying is available in case of an excess of gaseous ammonia,

while an evaporator comes on line when more gaseous ammonia

is needed. The pressure in the gaseous ammonia grid is maintained

exclusively by means of an evaporator operating on hot water.

The by-product aqueous ammonia from the synthesis plant is brought

up to the required concentration of 25 %, resp. 3.0 % in an

absorption unit where gaseous ammonia is added. Captive users

are supplied with 25 % ammonia solution via a pipe grid.

For delivery to outside customers a loading station for rail-

way tank cars and tank trucks has- been installed.

The system described above assures an optima! supply to all users.

4. Installations for Safety and Environmental Protection

Plant safety and environmental protection are closely interreiated

with questions of safe supply.

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The measures taken in this regard in the Ludwigshafen works

wil! be illustrated by the foTIowing examples.

4.1 Liquid Ammonia Grid

For the construction of the pi pel ine grid for liquid ammonia •

seamless pipe with a nomina! diameter up to 200 mm (7.9 in) and a«=-*sr ' " a

nomina! pressure rating of at least 40 bar (580 psi) has been

used, preferably welded together. Where flanged joints are

necessary, for instance adjacent to valves, metal rings with

inserted asbestos gaskets have been used. The grid is sub-

divided into sections by numerous remotely controlled quick-v

action shutoff valves, with the volume contained in each

section beeing not larger than 5 m (175 ft. .). In case

of a leak the segment in question can be separated immediately

from the remainder of the network. Only a smal! number of

users wil! be affected by each shutoff since the pipeline

network is almost completely looped. The siubdivision into

segments also facilitates the installation of branchlines

for new users. Expansion valves have^ejn__insta_lled before

and after each quick-action shutoff valve. When necessary,

the contents of the isolated pipeline segment can be emptied

through a metal hose into a neighboring, stil! operating

part of the pipeline, which is done by means of a mobile

pump belonging to the works fi re department. Hoses and the

pump are afterwards purged with bottled nitrogen.

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4.2 Pi pel ine Network for Gaseous Ammonia

The pi pel ines of this network with a nomina! diameter up to 600 mm

(23.6 in) and a nomina! pre'-sure of 10 bar (145 psi) are long-

itudinaüy welded and'provided with f!at flanges and flat rjjbber

gaskets,,JUJ- necessary expansion beüows are made of stainless

steel. Temperature measuring points at the connections to* '•

refrigeration plants trigger alarms in case of breakthrough of

liquid ammonia into the gaseous ammonia network. I f there is*.

a sudden surplus of ammonia, e. g. in case of a plant fai!ure

on the part of a user, the pressure in the network is aüowed

to rise temporarüy from 2 to 3.5 bar abs (28 to 50 psi). This

pressure increase reduces the evaporation of üquid ammonia

in the refrigeration units connected to the network and

simultaneously increases the rate of absorption in the pro-

duction facility for aqueous ammonia which is automatically

switched to fuil load. At the same time the repressurizing

compressors are started. Only when a pressure of 4 bar abs (57 psi)

should be reached, ammonia and injected steam wou!d be released

into the air through. safety valves.

4.3 Barge Loading Facüities and Pi pel i nes

At the loading doek in the harbor the remotely controüed

articulated loading arms are equipped with remotely controüed

quick-action valves and quick-disconnecting flanges. In critica!

situations, e. g. a fi re in the harbor, these permit the barges

to cast off immediately, The loading and unloading is watched

via monitors. Remotely controüed water guns are available to

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fight ammonia spil!s and flres in the harbor area. The long

distance between the harbor and the ammonia storage requires

special safety measures for the pumping stations and un-

branched l i nes connecting them. Thus the 4.2 km (2.6 miles) l;ong

pressurized ammonia pipeline of 150 mm (6 in) diameter is

subdivided by qutck-action valves into five sections, each

of which is protected by safety valves arranged in cascade.

Volume flow and pressure of the ammonia are adjusted

exact!y at the pumping station. Rapid changes in flow vel oeity,

such as may be caused by a sudden closure of the loading device,

can cause pressure surges (so-called "water hammer") that can

seriously endanger the system, mainly the loading arm and

the fittings on the barges. The occurrence of a "water hammer"

was simulated on a digital computer using generally valid

pressure transient equations as a basis (cf. V. L. Streeter,

E. B. Willie,."Hydraulic Transients", McGraw Hill, New york).

At the same time pressure surges occurring at the pumping station

and the loading arm after pump fai l ure or rapid closure of

a valve were measured for various flow rates with the ai d of a

fast respondingrecorder when the pipeline was put into service.

3 ?When the volume flow rate was 100 m /h (3500 ft./h) and the

quick-action valve at the doek was closed within 1.5 secs.,

which is certainly less than the 2.9 seconds required for the

pressure surge to traverse the pipeline, the observed pressure

peaked at 13 bar (185 psi) instead of the calculated 20 bar

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(284 psi). When this measurement was repeated after liquid

anmonia had been passed through the pi pel i ne for a "longer

period and the pressure at the loading arm had been

inv.reased by partly closing the valve on the barge, the

pressure surge was much more pronounced. This leads to

the conclusion that inert gases dissolved in the liquid

anmonia (hL» j CH,, A) have a certain cushioning effect.

4.4 Col d Annnonia Storage

Special care was taken in designing safeguards for the cold

ammonia storage.

Both doublé wal! tanks have been errected at a safe distance

from neighboring plants and storage vessels in a depression2

measuring 10 000 m (2.5 acres). Liquid ammonia leaking into

the space between the inner and outer tank wal!s can be

pumped into the other storage tank or into the pipeline

network. Liquid ammonia escaping into the open will collect

in a concrete pit, where i t can be pumped out. '

In case of disaster foamed polystyrene panels stored.nearby

can be used to cover large quantities of escaped cold ammonia.

For fighting ammonia clouds eight water guns with spray nozzles

have been permanently instalied. In addition the fire department

stationed nearby has available mobile foam and water guns and

water guards for raising water curtains.

'This pit is also very useful when during tank revisions the oilcollected in the tank bottom has to be separated from the washwater.

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In case of a power fai l ure the pressure in the col d storage

tank can be kept constant by means of a diesel-driven

reciprocating compressor. Besides both tanks are secured

against an excess pressure of up to 80 mbar (8QQ mm'- 31. in water

column) by means of a dipleg seal filled with oil. Gas

that escapes through this dipleg seal is drawn off with

steam-driven injectors and after dilution with air ten times

in excess and preheating is ejected at a height of 20 m (65 ft.)

above the roof. Because of the problems in connection with

pi lot fTame and NO -formation a fl are was not used.A

In one of the tanks the temperatures near the wal! and in

the center were measured at various leve!s over a period

of twelve years. These measurements showed only minor

- temperature differences (up to 2 °c[5,6 °F]). between the

layer and the surface, even at a high liquid level. The

danger of a "rol! over" thus seems very improbable.

Equipment for circulating the contents of the tanks was

therefore not considered necessary.

4.5 Tank Car Loading Station

Over and above the safeguards which are required by law for

atank car loading facility, such as scales, derailers, "car

connected" warning light, quick-action valves in the

connecting lines and tripwires to keep the bottom valves of

the tank cars open during filling, the following safety

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equipment was installed:

The entire filling process is steered and monitored by a

computer. A step-wise program and the storage of important

data concerning the tank car prevent operating errors during

filling and an overfilling of the tank cars. The rip cord

mentioned above unhooks if the car is moved accidentally and

automatically allows the bottom valve of the tank car, which

is being bottom-loaded through an articulated l dading arm, to

close. This tripwire can also be unhooked by remote control

in case of leakage. When this happens the quick-acting valves

in the connecting l i nes are closed, an alarm is actuated,

breathing air is routed into the weighing shed and a water

curtain is raised around the entire loading area.

4.6 General Safety and Environmental Protection Measures

The entire ammonia distribution is monitored and regulated from

a control room. The plants that surround the central plant are

interconnected by an emergency speaker system. On a wind speed

and direction indicator in the control room personnel can

immediately recognize in case of an emergency which plants are

endangered. Through a hook-up to the central alarm teletyper

of BASF all interna! ammonia consumers can be forewarned with

preprogrammed announcements in case of emergency. Our safety

program is complemented by regular drills with the fire

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department, where for instance the pumping of amnonia out of

a damaged tank car is practiced.

Speaker system, emergency shower, eye douche, respirator and

protective clothing are available in all parts of the plant.

AU control rooms and rest rooms are provided with emergency

breathing air.

Extensive measures have also been taken to keep air and water

clean. In various parts of the plant the air and the spent .

cooling and waste water are monitored by analyzers.

In order to minimi ze pollution during noraial operation, inert

gas mixtures which contain ammonia and which originate in the

ammonia storage vessels, in the repressurizing units and in the

loading stations are collected and fed into a cold storage tank.

Subsequently the gas is drawn off through a refrigeration unit,

scrubbed with water under pressure and,burned as boiler fuelThe air drawn off during filling cars with aqueous ammonia or

from the aqueous ammonia tanks is also scrubbed.

At this time we are engaged in improving noise prevention in the

plant.

For the future we consider i t important to deepen experience

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exchanges with and the flow of experience to our customers.

In concluding these remarks i t should not be omitted to

express thanks to all companies whlch have partlcipated actively

In the exchange of experience in the important area of safety in

the storage and distribution of ammonia and which have thus

contributed to obtain the best solutions.

Page 12

Typteal daiiy production and consumptionintonsNH3

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other inorg. products

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Page 13

ammonia synthesis plants

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Page 18

roof layers

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inside tank wall

tank B 2 Neopolen^plates withsteel bandages

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