Ammonia Storage & Handling

1

AMMONIA – ISANJAY JAIN

IntroductionIntroduction

Storage at ambient temperature and equivalent pressureStorage at ambient temperature and equivalent pressure in cylindrical in cylindrical vessels. This method is used when relatively small quantities vessels. This method is used when relatively small quantities (2.5 – 150 T)(2.5 – 150 T) are to be stored.are to be stored.

Storage under pressure in spherical vessels.Storage under pressure in spherical vessels. These can be constructed at These can be constructed at sites to hold several thousand tons of ammonia. However, very large sites to hold several thousand tons of ammonia. However, very large spheres are uncommon and most vessels are in the range of spheres are uncommon and most vessels are in the range of 500 to 3000 500 to 3000 tonstons. Refrigeration equipment may be used to lower the temperature of the . Refrigeration equipment may be used to lower the temperature of the ammonia and in such cases the vessels operate at lower temperature than ammonia and in such cases the vessels operate at lower temperature than ambient. This type of storage is often referred to as semi-pressure or semi-ambient. This type of storage is often referred to as semi-pressure or semi-refrigerated.refrigerated.

Storage at atmospheric pressure.Storage at atmospheric pressure. Ammonia can be stored at atmospheric Ammonia can be stored at atmospheric Pressure by reducing the temperature to –33Pressure by reducing the temperature to –3300 C. In this condition it may be C. In this condition it may be contained in cylindrical flat bottomed tanks, since the pressure, the tank contained in cylindrical flat bottomed tanks, since the pressure, the tank must withstand, is only imposed by the head of liquid. In practice, a slight must withstand, is only imposed by the head of liquid. In practice, a slight positive pressure is maintained to simplify the operation of refrigeration positive pressure is maintained to simplify the operation of refrigeration system. This method of storage is generally adopted when quantities system. This method of storage is generally adopted when quantities in in excess of 3000 tonsexcess of 3000 tons are involved. Many tanks have been built in the are involved. Many tanks have been built in the 20000 20000 – 35000 tons– 35000 tons range with few in excess of 35000 tons. range with few in excess of 35000 tons.

Three methods of storage of Liquid Ammonia are currently used, the choice Three methods of storage of Liquid Ammonia are currently used, the choice primarily depending on the quantity to be stored, economy and end use.primarily depending on the quantity to be stored, economy and end use.

2

Single walled tank:Single walled tank: This comprises of flat bottom tank with a dome This comprises of flat bottom tank with a dome roof designed to withstand the stated conditions. Tanks of this type roof designed to withstand the stated conditions. Tanks of this type will have external surfaces insulated to minimize heat gain from the will have external surfaces insulated to minimize heat gain from the surroundings.surroundings.

Double wall tank:Double wall tank: The outer tank is not designed to contain any The outer tank is not designed to contain any escape of liquid from the inner tank, its function being only to escape of liquid from the inner tank, its function being only to support and protect the insulation. The simplest form comprises an support and protect the insulation. The simplest form comprises an inner tank which is surrounded by an outer tank, from the roof inner tank which is surrounded by an outer tank, from the roof which is suspended an insulated deck designed to fit loosely with in which is suspended an insulated deck designed to fit loosely with in the shell of inner tank.the shell of inner tank.

Double integrity tank:Double integrity tank: This tank consists of double wall construction This tank consists of double wall construction with both tanks designed so that in the event of failure of inner with both tanks designed so that in the event of failure of inner shell the ammonia will be contained by the outer shell. The inner shell the ammonia will be contained by the outer shell. The inner tank is open topped and the insulation be applied to the exterior of tank is open topped and the insulation be applied to the exterior of the outer tank . The inter-space between the tanks will contain only the outer tank . The inter-space between the tanks will contain only cold ammonia vapor. A suspended deck type insulation cold ammonia vapor. A suspended deck type insulation arrangement may be used as an alternative to insulate the roof. arrangement may be used as an alternative to insulate the roof.

Atmospheric storage tanks:Atmospheric storage tanks:

Cylindrical flat bottom tanks, used for large storage of ammonia in fully Cylindrical flat bottom tanks, used for large storage of ammonia in fully refrigerated condition, may be divided into three basic types.refrigerated condition, may be divided into three basic types.

3

Liquid ammonia is received from the ammonia plant temp. of -330C. When ammonia is being transferred to the storage tanks, flash vapors are generated.

In normal operation, vapor blower K-7001 is always running to remove ammonia vapors generated due to ingress of heat to the storage tank & are sent to GP-II (Ammonia refrigeration compressor system) for condensation & liquid ammonia production; and only at the time when vapor blower (K-7001) is in maintenance/break down or in the event of build up of excessive pressure, these vapors taken to the refrigeration system (K-2001 A/B) for liquefaction and sent back to the storage tanks

Process Description

4

Ammonia Vapor from tank Ammonia Vapor

to Amm-2

From Tanks

PDIC 7001

Ammonia Blower K-7001

PV 7001

PGPG

PV7002

5

PIC 512

T 2001 B

Ammonia Storage

Ammonia to Urea

Ammonia Vapor

Flare header

HV 502 A HV 502BFlare

From A-1

Liquid Ammonia

From A-2Liquid Ammonia

EMV 507

EMV 506

PV 512

P-2001A P-2001B P-2001C

T 2001 A

HV 501

HIC 7001

T 2001 B

6

Loading/Unloading arm

Flare and drain systemFlare and drain systemFor disposal of vent ammonia vapor from ammonia tank For disposal of vent ammonia vapor from ammonia tank and equipment safety valves (except safety valve on and equipment safety valves (except safety valve on ammonia tank, which shall be vented directly to ammonia tank, which shall be vented directly to atmosphere), flare system is provided. atmosphere), flare system is provided.

Drain system is provided to drain the vessels for any Drain system is provided to drain the vessels for any maintenance. The liquid from drain lines from static maintenance. The liquid from drain lines from static equipments are sent to vent drum where evaporated vapor equipments are sent to vent drum where evaporated vapor ammonia from the top is released to flare header.ammonia from the top is released to flare header.

The system consists of vent drum, flare stack, NG supply The system consists of vent drum, flare stack, NG supply etc.etc.

7

Flare StackFlare StackFlare stack height is 30 M which is designed for ground level Flare stack height is 30 M which is designed for ground level radiation of maximum 1200 BTU/hr/ftradiation of maximum 1200 BTU/hr/ft22 and ground level and ground level concentration of 25 ppm ammonia and 30 ppm maximum concentration of 25 ppm ammonia and 30 ppm maximum NONOXX concentration. It consists of 2 pilot burners, one flare tip concentration. It consists of 2 pilot burners, one flare tip and automatic flare front generation. Flare stack is also and automatic flare front generation. Flare stack is also provided with labyrinth seal, which prevents ingress of provided with labyrinth seal, which prevents ingress of atmospheric air into the flare line by reversing the fluid path. atmospheric air into the flare line by reversing the fluid path. Water seal is provided for labyrinth seal and riser pipe to Water seal is provided for labyrinth seal and riser pipe to drain any rain water that may enter.drain any rain water that may enter.Natural gas is used as pilot gas. Natural gas is used as pilot gas. Supply rate : 6 Nm Supply rate : 6 Nm 33/hr./hr.Auto ignition temperature of ammonia: 651 Auto ignition temperature of ammonia: 651 00CCExplosive range of ammonia: 16-25 %.Explosive range of ammonia: 16-25 %.To minimize the hazard, a small amount of nitrogen or To minimize the hazard, a small amount of nitrogen or natural gas is continuously purged to flare header.  natural gas is continuously purged to flare header.  2 NH2 NH3 3 + 3/2 O + 3/2 O2 2 ---- ---- N N2 2 + 3 H+ 3 H22 O OBut there is some possibility for generating some undesirable But there is some possibility for generating some undesirable oxides of nitrogen.oxides of nitrogen.

8

99

250 mmWC to 2.7 Kg/cm2 g

T-2001

K-2001 A First Stage

10

T-2001

K-2001 First StageFlash Vessel

11

2.5 Kg/cm2 g to 16 kg/cm2 g.

T-2001

K-2001 First StageFlash Vessel K-2001 Second Stage

12

Condenser

13

Receiver

14

15

16

Flare

17

Ammonia Vapor from T-2001 A/B

K-7001

PV 7002

PIC 7002

Ammonia Vapor to AMM-II

K-2001 A/B

1 2

Saturator

V-2001 V-2002

Flash Vessel

E-2001 A Condenser

E-2001 B Condenser

CW CW

CW

V-2001 Receiver B-2001

KO Drum

PV 509

PIC 509

LIC 504 LIC 505 LIC 506 PIC 511To Flare Header

18

19

1900

0 0u

ter

shel

l Hei

ght 25000 ID outer shell

23400 ID inner shell

6 mm Thick Single Tap Welded Dome Roof

Ground Level

Bottom Insulation 200 Foam Glass bricks and 25 mm thick Sand Layer

Foundation

Poly Urethane Foam Shell Insulation 210 mm Thick

Outer Shell Stiffener

3.6 Thick Suspended Deck

250 Thick Fiber Glass Deck Insulation

1800

0 In

ner S

hell

Hei

ght

1752

0 M

ax L

iqui

d Le

vel

Storage Tank T-2001 A/B

20

1 Storage capacity 2 x 5000 Tons of liquid ammonia at -330C temp.

2 Normal Op. pressure of tank + 350 mmWC

3 Range of operating pr. of tank +200 to +800 mmWC

4 Design pressure of tank + 1050 mmWC

5 Design vacuum of tank - 50 mmWC

6 Safety valve pr. setting + 1050 mmWC

7 Vacuum relief valve setting - 50 mmWC

8 I.D. / Height (inner shell) 23.4 M / 18.0 M

9 I.D. / Height (outer shell) 25.0 M / 19.0 M

10 Insulation Shell - PUF

Suspended Deck - Fibre Glass

Bottom - Foam Glass

Storage Tank Specifications

These storage tanks are of double wall, double integrity design (steel cup in steel tank) and outer tank shell is designed to contain entire liquid ammonia in the event of failure / leakage in inner tank

21

Ist stage: (design)Suction : 0.96 Kg/cm2 A / -20 0CDischarge : 4.8 Kg/cm2 A./ 106.5 0CCapacity : 621 Kg/hr.

 2nd stage: (design)Suction : 4.6 Kg/cm2 A / 1.5 0CDischarge : 20.66 Kg/cm2 A./ 121.68 0CCapacity : 883 Kg/hr.

Ammonia Compressor K-2001 A/B

Service: To compress vapor ammonia from tank during holding duty and unloading from plant.

22

Intermediate Flash Vessel: (V-2002)

Service: To saturate the compressor first stage discharge before compression in second stage by bubbling the vapors through liquid. Liquid is taken from V-2003 and returned to T-2001.

Operating Pressure : 3.8 Kg/cm2 gOperating temperature : 1.5 0C (max)Design Pressure : 25 Kg/cm2 gDesign Temperature : - 34/60 0CI.D. : 700 mmLength : 2500 mmMaterial of construction :LTCS.Insulation : PUF

23

Type : Vertical, Barrel, Multistage, centrifugal.Capacity : 47 M3/hr. (32 tons/hr)Minimum Continuous Flow: 10 M3/hr.Discharge Pressure : 25.55 Kg/cm2 gEfficiency : 56.4 %Material (case/impeller) : LTCSMotor (KW/rpm) : 75 / 2900Insulation : PUF (cold) No. of stages : 10

Ammonia Pumps P-2001 A/B/C

Service : To dispatch liquid ammonia to plant battery limits. The suction and discharge headers of pumps are designed for a combine flow of 69 MT/hr. The pumps can also transfer liquid ammonia from one tank to another tank through plant ammonia unloading line. The minimum flow to the pump suction is assured by minimum flow line. A part of the discharge is sent to the tank via ARC (Auto Recirculation Control) valve and minimum flow line when pump operates with discharge valve closed condition.

24

Ammonia Blower K-7001

Capacity : 1719.6 Nm3/hr.

Inlet Volume Flow: 1654.43 Nm3/hr.

Temperature : -33 (min), -10 0 C (normal).

Pressure: 100 (suction)/ 1140 (discharge) mmWC g.

Differential Pr. : 1040 (rated) mmWC g.

Speed : 2940

Power : 9.8 KW.

MOC : case – LTCS, internals - SS

Impellers : 1,

Dia : 980 mm

Blades : 14

Driver : Induction Motor, 22 KW, 415 V, 50 Hz.

25

26

(1)  Instrumentation of high reliability have been used viz. two independent systems for the important measurements such as tank pressure, level and temperature.

(2)    Dependable alarms and interlock system for critical parameters.

(3)    Flare system availability to take care of excess pressure build up by venting & burning ammonia vapors manually or automatically through HV-502 A/B.

(4)    Reliable safety valves to take care of any build up of pressure in the tank beyond a pressure of +1050 mmWC.

(5)    Installation of Ammonia detectors( 7 nos.) at specific locations for detection of amm. leak in storage area.

(6)   Arrangement of water spray at tank top and water curtains around compressors house, ammonia transfer pumps & B/L I/Vs to control the leakage of ammonia at the source.

Safety

27

PRESSURE / TEMP. AND LEVEL CONTROL FOR AMMONIA STORAGE TANKS

1)      PRESSURE AND TEMPERATURE CONTROL

Under normal conditions, pressure control of vapour in the tanks is achieved through the vapour blower, which discharges the vapour into the suction of Amm-2 refrigeration compressor system for compression & condensation of liquid ammonia. This operation takes care of flash vapours generated during transfer of ammonia to the storage tanks from ammonia plant & vapours generated as boil off.

The Vapour blower K-7001 (having rated cap. of 1320 kg/hr) has the capacity to handle the max. vapours generation, calculated as 1307 kg/hr considering total ammonia production @ 150 T/hr of GP-I & II is transferred at -320C temperature when all four streams of urea trips .

28

In the event of build up of excessive pressure (above +750 mmWC) due to

(1) Failure of Vapour blower/refrigeration system or,

(2) higher rate of transfer of liquid ammonia from ammonia plant- I & II resulting in higher generation of flash vapour or,

(3) Damage to insulation resulting in higher boil off,

Venting is done to flare stack through vent control valves HV-502 A & B (Cap.595 kg/hr each) to bring the normal pressure in the tanks and to make the conditions safe from any untoward release of ammonia vapors in the atmosphere. In addition to this, two nos. 12" x 16" safety relief valves (having relieving cap. of 25,470 kg/hr & set pressure +1050 mmWC) and four nos. 8” vacuum relief valves (suction cap. 3763 kg/hr) have been provided on each tank. The safety valves are designed to release ammonia vapours that may get generated due to any external fire around the tanks. While the vacuum valves protect the tank from vacuum due to failure of safety interlocks or reliquification system. These safety relief valves and vacuum relief valves are mounted on three-way valves in such a way that even if one safety/vacuum relief valve is isolated for maintenance the other valve remain lined up with tank.

29

If the level in storage tank is Very High, the level high alarm and interlock I-103 will close the control valves PV-512 on the wagon/truck unloading line and HV-501 & HV-7001 on the liquid ammonia transfer line from plant – I & II. Similarly, in case of Very Low level in the tank, the level low alarm and interlock I-104 A/B will close the respective tank outlet valves (i.e. EMV-506 / 507).

2) TANK LEVEL CONTROL

Level Measuring System: Ø      Inner Tank is provided with - Servo type Float operated Level gauge - Differential Pressure type Level transmitter

Ø      Outer tank is provided with - Differential Pressure type Level transmitter

30

Pressure/Temperature Measuring/Monitoring System: Normally the pressure/temperature in storage tank is maintaining between 200 mmWC and 550 mmWC and -33o C. The tanks are provided with Ø      Pressure transmitter: used for recording the pressure of the tankØ      Pressure switches: used for compressor loading and unloadingØ      Interlocks: To trip compressor and pumps on very low tank pressure.Ø      The tanks are provided with Pressure gauge on each tank top, a common PG at tank bottom, one pressure indicating recorder for each tank and one pressure indicating controller are provided in control panel. Two number of multipoint temperature recorder are provided to record liquid ammonia temperature in storage tank and re-liquification system.Ø      Pressure relief valves and Vacuum relief valves (Three way valves): protects the tank from over pressure and vacuum incase of failure of safety interlocks or reliquification system. These are mounted on three way valves in such a way that if one pressure or vacuum relief valve is isolated for maintenance the other valve remains lined up with tank.Ø      The tank pressure can be controlled by manual venting device HIC-502 A/B. when the tank pressure is high, the operator can manually vent vapor ammonia to flare stack H-2001.

31

1. Level alarm:• If the level in the storage tank is very high, the level high

alarm and interlock I-103 will close the control valves PV-512 on wagon/truck unloading line and HV-501 in the liquid unloading line from plant.

• In case of very low level in the tank, the level low alarm and interlock I-104 close the respective tanks out let valves.

I-104 A closes EMV-506I-104 B closes EMV-507

If both the tanks level Is very low then both EMV-506 and EMV-507 are closed and this leads to the tripping of all the ammonia pumps.

 

Alarm/Interlock Logic System:

A. Storage Tanks

32

2. Pressure alarm          · If the pressure in the tank is very high (805

mmWC), the pressure high alarm interlock I-102 will close the control valves HV-501, HV-503, PV-512 and opens the tank vents HV-502 A/B. This will lead to the closing of liquid/vapor inlets to the tank and venting of ammonia vapor from tank to flare.

· In case of pressure falling very low (150 mmWC), I-101 will stop the ammonia pumps P-2001 and stops the compressor.

33

I-101 stops the pump in case of very low pressure in tank. I-105 stops the pump if both tank outlet valves are in closed condition. I-106 Awill stop the pump P-2001 A in case of low

differential pressure across the pump (25 Kg/cm2 g)

I-106 B will stop the pump P-2001B in case of low differential pressure across the pump

I-106 C will stop the pump P-2001 C in case of low differential pressure across the pump.

Interlocks - Ammonia Pumps

34

I-101 stops the compressor in case of very low pressure in tank.

I-107 trips the compressor in case of high liquid level in the ammonia saturator V-2001.

I-108 trips the compressor in case of high level in the intermediate flash vessel V-2002.

I-109 trips the compressor in case of low cooling water flow to the condenser E-2001 A/B.

I-111 A/B Trip respective Comp. K-2001 A/B if the First stage suction pressure is low. (-400 mmWC)

I-112 A/B Trip respective Comp if first stage discharge pr. Is high. (4.2 Kg/cm2 g)

I-113 A/B Trips respective Comp. K-2001 A/B if second stage discharge pressure is High (20.56 kg/cm2 g)

I-117 A/B Trips the respective Comp. K-2001 A/B if the lube oil pressure is very low. (0.35 Kg.cm2 g)

Interlock - Ammonia compressor:

35

36