低温液体贮槽使用说明书英文版

Cryogenic Liquid Tank Operation and Maintenance Manual

HangZhou Chuankong General Equipment Co.Ltd

2007

Contents

I.Structure Description

II.Operation and Maintenance

1.Operation

2.Maintenance

III.Transportation and Installation

1.Transportation

2.Installation

IV.Safety Requirements and Precautions

1.Safety Requirements

2.Precautions

I.Structure Description

1.Main Structure

The tank is of double-wall structure. Its inner vessel and piping are made of austenitic stainless steel while its outer vessel is made of carbon steel Q235-B. The jacket between the inner and outer vessels is fully filled with perlite and evacuated. A specially treated adsorbent is placed

in the jacket to prolong the vacuum life of the tank.

The tank is equipped with various valves around its bottom for operating it.

The tank is equipped with pressure gauges and liquid level gauge for indicating the pressure and liquid level in the tank.

2.Peculiarities

(1)Compact structure and less occupied space;

(2)The tank and its booster combine into a closed system and thus the liquid

or gas may be delivered out without adding any external power so that

the purity of the liquid or gas can be ensured.

(3)The tank is equipped with the pressure adjusting device and the user can

deliver the cryogenic liquid with a required pressure according to his

request; moreover the pressure is stable and the operation is easy;

(4)The tank is equipped with the liquid filling connector for filling the liquid

to the cryogenic liquid vaporizers and tankers;

(5)The perlite (thermal insulation material) and adsorbent used for the tank

have been specially treated so as to prolong the vacuum life. Moreover, the tank is equipped with a metallic thermocouple gauge tube for

measuring the vacuum in the jacket when necessary.

II.Operation and Maintenance

1.Operation

(1) Preparation

Before being put into service, the tank must be subjected to a gas-tight test,

a purging and a check for the valves and instruments.

①Gas-tight Test

The tank must be subjected to a gas-tight test before the cryogenic liquid is filled after the tank is installed or the temperature of the inner vessel is returned to the normal temperature. The test pressure should be the MAWP (maximum allowable working pressure) of the tank and the testing gas should be oil-free and dry air or dry nitrogen.

The testing time must be four hours or more.

②Purging

After the gas-tight test is accepted, the inner vessel system of the tank must be purged with oil-free and dry air or nitrogen to remove any moisture. After purging with the dry air or nitrogen, the whole system must be further purged with the product gas until the discharged purging gas reaches the required purity.

③Checking for Valves and Instruments

Make sure that all the valves are in correct opening or closing state and that all the instruments are in correct indication, otherwise they must be adjusted properly before the cryogenic liquid is filled.

(2) Liquid Filling

The liquid filling is divided into the first filling and make-up filling.

①First Filling (i.e. the filling when the inner vessel is at the normal

temperature)

The filling steps are as follows:

a)Connect the liquid filling pipeline.

b)Purge the liquid filling pipeline (this step must be done before

each filling). Before the liquid inlet valve is opened, the

liquid transferring pipe must be filled with a small quantity of liquid via the liquid discharging valve and at the same time the residual liquid draining valve must be opened to purge the pipeline for eliminating the moist air and General impurities from it.

c) Open the vent valve, the fullness measuring valve and

pressure gauge valve and start the liquid level gauge.

d) Open the upper filling valve to fill the liquid from the top.

Because the inner vessel is now at the normal temperature,

the valve must be slightly opened in order to cool the

pipeline and inner vessel gradually to the temperature of the

filled liquid. When the vapor is stably discharged from the

vent valve, the filling valve may be further opened to

increase the speed of filling.

e)When the liquid level gauge begins indicating a liquid level,

open the lower filling valve and close the upper filling valve to change the filling from the top into the filling from the bottom. f)When some liquid is sprayed from the fullness measuring

valve which is already opened, it means that the tank has been fully filled with liquid and then the lower filling valve should be immediately closed to stop the filling. At the same time the residual liquid draining valve should be opened to drain off any residual liquid from the liquid filling pipeline.

g) Disconnect the liquid filling pipeline upon completion of the

liquid filling.

②Make-up Filling (i.e. the filling when the inner vessel is at the

temperature of the cryogenic liquid)

The steps for the make-up filling are almost the same as those for the First Filling. The only difference is that some cryogenic liquid already exists in the inner vessel and that it is unnecessary to cool the inner vessel. Therefore the liquid may be filled directly from the lower filling valve after the pipeline is purged. In addition, from the viewpoint of pressure, the liquid filling may be divided into the filling without pressure and the filling with pressure:

●Filling without Pressure-------During this filling, the vent valve

is always opened to make the inner vessel communicate with the atmosphere. Therefore it is also called the filling under the normal pressure.

●Filling with Pressure------ During this filling, the vent valve is

closed and the pressure in the tank is higher than the atmospheric pressure. Therefore it is also called the filling under pressurization. However, the pressure in the inner vessel should not be higher than the maximum allowable working pressure of the tank during this filling.

The first filling must adopt the filling without pressure, while the

make-up filling may adopt the filling with pressure.

For the relation between the liquid volume and the liquid level, see the curve diagram plate mounted on the tank.

(3) Boosting

①Close the vent valve.

②Make sure that the gas passing-through valve is already fully

opened.

③Slowly open the boosting valve to let the liquid enter the booster

for vaporizing.

④The boosting valve may be further opened if the speed of liquid

discharging is too high and the pressure in the inner vessel is

decreased.

⑤The boosting valve should be closed when it is unnecessary to

stabilize the pressure in the tank or the liquid supply is stopped.

During the boosting, the pressure in the tank will be automatically kept stable because of the equipped pressure-rising adjusting valve.

When the first boosting is performed (or when it is necessary to

change the working pressure of the tank), the opening and closing

pressure of the adjusting valve should be adjusted to the required

value. The closing pressure of the adjusting valve should be equal to the required working pressure. The opening pressure of

the adjusting valve may be increased by tightening the adjusting

bolt at its top and decreased by loosening the bolt.

(4) Liquid Discharge

There are two types of liquid discharge:

①Discharge of Liquid to Vaporizer

When the pressure in the tank reaches the required value, the

liquid discharge valve may be opened to discharge the liquid to

the vaporizer.

②Discharge of Liquid from Liquid Inlet/Outlet Valve

The liquid is discharged to a tanker or other bigger tank via the

liquid filling hose. Its operating steps are basically the same as

those for the liquid filling, but the lower liquid inlet valve is

used for discharging the liquid instead of filling the liquid.

(5) Liquid Storage

The liquid storage is divided into the storage in normal pressure

and the storage in higher pressure:

①Storage in Normal Pressure

During the storage in normal pressure, the vent valve is always kept open to let the gas naturally evaporated vent to the atmosphere from this valve and to avoid the rising of the pressure inside the tank.

②Storage in Higher Pressure

During the storage in higher pressure, the vent valve is closed.

Because the gas naturally evaporated remains in the tank, the

pressure in the inner vessel is gradually increased. The liquid

level gauge and pressure gauges should be now put into operation.

When the pressure in the tank reaches the working pressure, the

vent valve must be opened immediately to release the pressure.

When liquid oxygen is stored in the tank for a long time (no matter

what type of storage is used), the content of hydrocarbons in the

liquid oxygen must be checked periodically so as to avoid any

accident, the main purpose of which is to check the concentration

of the acetylene. The concentration of acetylene must be less

than 0.5 ppm, otherwise the liquid in the tank must be thoroughly

discharged or some liquid oxygen must be made up to let the

acetylene content be less than 0.5 ppm.

Note: No matter the storage in normal pressure or the storage in higher pressure is used, the gas passing-through valve must be always

fully opened to ensure the safety valve work in normal condition.

Only when the three-way valve needs to be repaired, the gas

passing-through valve is closed and the vent valve should be

properly opened to avoid exceeding of the maximum allowable

working pressure in the inner vessel.

2. Maintenance

(1) Insulation Performance Protection

For the cryogenic liquid storing and transporting equipment, the most

important requirement is that they should have a good insulation

performance and a low boil-off of the cryogenic liquid. The vacuum

is the key point of the insulation performance. The thermal

conductivity of the perlite at normal temperature and pressure is 0.045 kcal/m.h.K while that at the vacuum of 66.66 ~ 1.33 Pa is 0.00225

kcal/m.h.K. So we can see that under the same other conditions the

heat transfer difference is 20 times depending on the jacket vacuum

(transferred heat: Q = KF△t1-1).

Whenever the vacuum is deteriorated, it is impossible to store the cryogenic liquid in the tank, so a lot of attentions should be paid to the vacuum of the tank. The outer vessel anti-explosion device and the

evacuating valve are directly communicated with the vacuum jacket. It is not allowed to dismantle them if the vacuum is not deteriorated or it is

unnecessary to make up the perlite and to re-evacuate the jacket. The evacuating valve is lead-sealed and it is prohibited to remove the valve at random.

The outer vessel is an external pressure vessel and subjected to the atmospheric pressure and thus no striking or bumping is allowed to avoid any damage to the outer vessel. It is not allowed to place the tank in the area where the temperature is higher than 50oC, otherwise the vacuum will be affected and the insulation performance will be lowered.

(2) Vacuum Examination and Re-evacuation

The vacuum of the tank shall be checked every half a year in general.

When measuring the vacuum, remove the cover of the metallic thermocouple tube and insert the plug of the thermocouple vacuum gauge, thus the vacuum level in the jacket can be measured. For details, refer to the operation manual of the thermocouple vacuum gauge.

After several years' operation, the vacuum may drop to the value lower than 67 Pa and it is necessary to re-evacuate the jacket to improve the insulation performance. Before re-evacuation, the liquid in the tank must be discharged entirely and then the tank must be warmed and purged with dry and oil-free air or the gaseous nitrogen at 80~100oC until it recovers to the normal temperature. Upon completion of connecting the evacuating piping, the pump must be firstly started for pumping out the moisture in the air of the vacuum pipe and then the vacuum valve may be opened for

re-evacuating.

For the details of evacuation, if necessary, the user can contact with the tank manufacturer. Both parties can decide through discussion the specific procedure of evacuation.

(3) Checking and Troubleshooting

①Normal Checking

a)Make sure that the valves are in proper opening/closing position;

b)Make sure that the measurement of the pressure gauges and liquid

level gauge is correct and reliable;

c)Make sure that there is no leakage or blockage in the piping and

valves;

d)When the pressure in the tank gets to the opening pressure of the

safety valve but the valve does not work, the opening pressure of

the valve must be calibrated immediately to insure the safety of the

tank.

②Periodical Checking

a) The pressure gauges shall be calibrated once half a year;

b) The safety valve shall be calibrated once a year;

c) The opening/closing pressure of the pressure adjusting valves shall be

calibrated once a year;

d) The vacuum in the jacket shall be measured every half a year;

③Trouble-shooting

For the details of troubles that may possibly occur during operation and

their cause and remedy, see Table 1. Table 1. Troubleshooting

III. Transportation and Installation

3.Transportation

(1) After the tank is arrived at the railway station or special railroad, the

operating personnel who unload the equipment from the train wagon

shall prepare the unloading procedure beforehand together with the

equipment manager.

(2)Rolling of the tank is not allowed at any time. The saddle for

transportation may be removed only after the tank is positioned for

installation.

(3)If transported by road, the tank must be tightly fixed with the truck

and the truck must be driven at a medium speed. No crashing

or bumping between the tank and any other object is allowed.

2. Installation

(1)After the tank is transported to the job site, the package for it may be

opened only after the requirements for the installation are satisfied.

During installation, any striking is prohibited and special care must be taken to protect the explosion-proof device of outer vessel and the vacuum valve.

(2)The deviation of verticality of the tank to the ground must be no more

than 1/1000.

(3)The inner vessel system of the tank shall be charged with dry nitrogen

to the working pressure to perform a gas-tight test. There must be no

any leakage in the valves, piping and flanges. Now the installation is

completed.

(4)For the installation dimensions, see the General Drawing (As-built

Drawing). If a tanker is used for filling and unfilling the liquid, the

road for the tanker should be taken into consideration.

(5)When the foundation is preparing for the tank, the drainage ditches

shall be made around the tank, booster and vaporizer for draining the

frost and water.

(6)The load-bearing capacity of the foundation shall be decided by the

civil engineer in the light of the full weight of the tank (i.e. the weight

of tank fully filled with the cryogenic liquid). The foundation

dimensions shall be decided by the user according to the load-bearing

capacity of the foundation and the actual geological condition of the

jobsite.

3. Stopping Use and Re-using

(1)If the tank is going to stop working for a short period of time, the

cryogenic liquid should not be entirely discharged in order to avoid the trouble of treating when it is re-used.

(2)If the tank is going to stop working for a long period of time for the

reason other than maintenance, a pressure of about 0.02 MPa must be kept in the inner vessel with the product gas.

(3)If the cryogenic liquid has been entirely discharged from the tank for

conducting the reparation or maintenance, the tank must be subjected to a gas-tight test (and to a vacuum leakage detection if possible). Then the tank must be purged and accepted by the inspection before it is re-filled with high-purity cryogenic liquid.

IV. Safety Requirements and Precautions

1. Safety Requirements

The safe operation of the cryogenic tank should be considered according to the gas properties, cryogenic temperature and pressure vessel.

(1) Properties of Gases and Their Cryogenic Liquids

Some properties of oxygen, nitrogen and argon are listed in Table 2.

When operating the tank, the operator must be thoroughly familiar with the properties of these gases in order to take the proper safety measures for the different cryogenic liquids.

Table 2: Some Properties of Oxygen, Nitrogen and Argon

All the O2, N2 and Ar are colorless, tasteless and non-poisonous gases.

O2is a strong oxidant and combustion-supporting matter. The oxygen-enriched air (O2content >21%) will cause fire and explosion.

N2 and Ar may cause suffocation and anesthesia to human beings.

(2) Requirement of Installation Site for Cryogenic Liquid Tanks

①Good ventilation is needed. The tanks with a capacity more than 500

L should be installed outdoors.

②There must be no any opening to any lower places (e.g. basement,

cellar, underground well, ditch, etc.) within 5 meters around the tank.

Otherwise there should be a liquid-blocking weir around the

opening.

③The tank must be located more than 7.5 m away from the

densely-populated area (e.g. offices, public roads and public places).

④The LO2 equipment must be located no less than 30 m away from

the inflammable buildings and no less than 15 m away from the

fireproof buildings. Moreover there must be no any door of the

buildings towards the equipment.

⑤No smoking or fire source may exist at least within 5 m around the

LO2 equipment (including the storage tank, vaporizer and pressure

reducing device, etc.) and no electrostatic spark in the operation area

is allowed.

⑥The tank should not be located in a low-lying land or basement.

Otherwise the good ventilation must be provided so excellently that

the liquid and gas must be able to be discharged away absolutely

safely when any fault happens.

⑦The gas vented and the liquid discharged when a fault occurs must

be sent to the specific safe area. The indoor-installed safety valves and vent valves must discharge the gas or liquid to the outdoor safe area.

(3) Relation between Tank Capacity and Liquid Temperature

The density of the cryogenic liquid will be decreased with the rising of its pressure, so the capacity (weight) of the tank will be reduced with the rising of its saturation temperature. During the liquid filling and storage with pressure, it is not allowed to exceed the permitted capacity (volume) at its corresponding saturation temperature (i.e.

under any cases it is not allowed to exceed the volumetric liquid filling rate of 95 %).

(4) Safety Requirements during Operation and Maintenance

①The opening and closing of the valves must be conducted slowly to

avoid the occurrence of sparks.

②The liquid storage with pressure should be performed on the basis

of being familiar with the relation between the pressure rising and

time changing. And the safety devices must be stable and reliable.

③The valves and pipes newly repaired or replaced must be degreased

completely before they are reassembled or installed.

④Before conducting of any repairing or welding, all the liquid must

be thoroughly discharged from the tank and the tank must be warmed and purged with oil-free and dry air. The welding for the equipment may be conducted only after the O2content in the atmosphere in the tank is 21% approximately.

⑤Before any personnel enter the room enriched with O2, N2 or Ar,

the room must be completely ventilated and purged.

⑥The skin of any operator must not be contacted with the cryogenic

liquid. When operating, he (she) must put on the appropriate

protection wears.

(5) For the other safety requirements for operating the cryogenic liquid

tanks, refer to the standard JB6898 “Safety Rules for Operation of

Cryogenic Liquid Storing and Transporting Equipment” and the

other related regulations.

2. Precautions

(1) Whenever the boosting is not needed during the period of the liquid

storage, the boosting valve should be closed tightly to avoid a higher

evaporation loss of the cryogenic liquid because of the possible

internal leakage of the boosting valve.

(2) The cryogenic liquid should not be entirely discharged from the tank in

general during operation in order to prevent the temperature inside the tank rising to the normal temperature and to avoid too much liquid loss during the refilling. If the storage tank is to be put out of service for a long time, all the liquid should be discharged from the tank and all the valves must be closed to keep the pressure inside the tank at approximately 0.02MPa to prevent any damp air or dust from entering

the tank and to avoid blocking the pipes & valves or affecting the gas purity.

(3) In case of changing the cryogenic liquid stored in the tank, the tank

must be purged first with oil-free and dry air or nitrogen to remove the original residual liquid in the tank thoroughly and then displaced with the new product gas which is to be stored in the tank.

(4) The inner vessel has been already filled with dry nitrogen at 0.02 MPa

for protection. It is not allowed to discharge the nitrogen gas out of the vessel before it is put into use.

(5) The operation and maintenance of the level gauge and other matched

instruments should be conducted as per their own operation manuals.