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Applies to:

Functional /Domain Experts

Summary

This paper describes LPG filling operations in a LPG Bottling Plant.

Author(s):  

Vimal Chandra

   
Company:     Infosys Technologies Ltd
Created on:    06/10/2009
Author(s) Bio
Vimal Chandra is working as Senior Associate Consultant in Infosys Technologies Ltd. He has got more than 6 years of experience in Oil & Gas domain while working for Fortune 500 Oil Marketing and Refining Company .

OVERVIEW OF PLANT OPERATIONS IN LPG (LIQUIFIED PETROLEUM GAS) BOTTLING PLANT

LPG bottling plant is a plant where LPG is filled into bottles (cylinders)  for storage  and distribution among  various LPG distributors. The plant has the facility to receive bulk LPG by Tank trucks (of various capacities e.g. 12MT, 17MT etc) or pipeline from a reliable source e.g. Refinery or any other LPG Bottling Plant.  After receipt of Bulk LPG, filling of LPG into cylinders is done. Here we shall discuss the filling operations in LPG Bottling Plant.

SEQUENCE OF PRIMARY OPERATIONS
OVERVIEW OF PRIMARY OPERATIONS:
Primary Operations in a Bottling plant are main line activities, directly associated with filling of LPG cylinders. Any obstruction in these activities will hamper Plant production. Some activities are Cylinder receipt, filling, Check scale weighing, Tightness testing etc. These are described below :
STAGE - I: RECEIPT OF CYLINDERS
Explanation:
(a) Incoming cylinders fall into following categories:
(info) New cylinders from manufactures
(ii) Cylinders in circulation from distributors (empty, under-filled, defective).
(iii) Cylinders received from Statutory Testing Plants, duly tested.
(iv) Repaired cylinders received from the approved repairers.
(b)  All cylinders received should be against valid documents and the actual receipt should be   tallied with the details on the relevant document and shortages or any other shortcomings   should be endorsed on the body of the document.
(c)  All new cylinders received should be supported by Test Certificate for ISI (Indian Standards Institute) inspection and    approval from CCE (Chief Controller of Explosives)  before they are put to use.
STAGE -II: VISUAL INSPECTION/SEGREGATION - I
Explanation:
(a)     Based on visual inspection, cylinders should be segregated as under:
i. Cylinders for Statutory Testing (to be sent to testing Plant).
ii. Under-filled cylinders received from distributors, duly tagged (for further processing).
iii. Leaky/defective cylinders received from the distributors, duly tagged (for further   processing)
iv. Spurious cylinders (for investigation/scrap).
v. Cylinders found unfit for filling (beyond repairs) on visual inspection (e.g. heavily rusted  or heavily dented).
vi. Cylinders found defective, but repairable such as:
a. Cylinders having twisted valve spindle (to be segregated for valve replacement)
b. Cylinders having broken/bent foot ring/valve protection ring (to be segregated for cold/hot repairs depending upon the condition).(To be rejected as scrap after closer re-examination).
vii. Cylinders owned by other marketing companies, wrongly mixed with own cylinders.   (to be segregated for handing over to OMC).
viii. Empty cylinders fit for filling. (to be sent for filling).
(b)     Visual inspection of the cylinders should be done.
(c)     Under-filled cylinders received from the distributors should be weighed to verify the extent of under-filling.
(d)     Reasons for leaky/defective cylinders received from distributors should be verified as marked on the tag          attached to the cylinder.
(e)     Extra care should be exercised to check for spurious cylinders and efforts made to identify the source of receipt. Spurious cylinders must be segregated for scraping.
(f)       New cylinders or cylinders received from Statutory Testing Plant or any cylinder which has undergone pneumatic test must be purged before they are taken up for filling.
(g)     Cylinders due for Statutory Testing must not be taken up for filling but sent to testing Plant.
(h)     Cylinders without proper markings or without serial number should not be taken up for filling.
(info)       Cylinders of other marketing companies, unless specifically sent for filling, should not be taken up for filling but segregated for exchange with concerned marketing company.
(j)       Wherever on-line facilities on the conveyor for cleaning and re-painting of cylinders are provided within the filling Plant, segregation for these operations also would be necessary.
(k)      At the time of visual inspection during unloading, check should be made for shortage of removable items such as valve protection caps, security nuts, safety caps, etc., and appropriate remarks put on the relevant transfer documents.
STAGE - III: CYLINDER FOR FILLING.
Explanation:
(a)     Remove valve protection cap wherever provided on the cylinder.
(b)     Remove safety cap in case of 'SC' type valve (Self Closing Valve).
(c)     Blow the cavity of 'SC' type valve with air to remove any dust particles or water and also check for the presence of 'O'-ring fixed on the valve outlet.
STAGE - IV: TARE WEIGHT MARKING
Explanation:
(a)     Wherever tare weight stenciling is not legible on the cylinder shoulder, mark tare weight on the cylinder shoulder after checking punched tare weight marking on the cylinder.
(b)     For accuracy of filling, especially in case of filling through overall-weight-system, the correct and legible marking of tare weight on the cylinder body is essential. To ascertain the accuracy of tare marking on the incoming LPG cylinders, few cylinders should be weighed at random. This exercise should invariably be carried out on the new cylinders. In case any major discrepancies are observed in a particular lot the matter should be taken up with the manufacturer.
(c)     Tare weight, in case of cap type cylinders, is exclusive of the weight of the cap. In case of cylinders with shroud or ring as valve protection means, the tare weight includes the weight of the shroud or the ring as they form integral part of the cylinder.
STAGE - V: FILLING OPERATION
Explanation:
(a)     Cylinder with 'SC' type valve.
i. Fix appropriate filling head on to the valve.
ii. Start filling.
iii. Make tare-weight adjustment.
iv. Remove filling head on automatic shut-off the filling operation.
(b)     Each filling machine should be checked against standard weight at least once during a shift.
(c)     The above sequence of operations of operations has been described for filling machines having adjustment for 'tare weight' as well as 'specific weight" for the product (i.e. LPG)
(d)     In case the filling machines operate on 'gross weight' principle, the adjustment required on the machine would be for gross weight only.
(e)       In case the filling machines operate on 'tare-off' principle, no adjustment may be required. However, in this case it must be ensured that the cylinders are evacuated or safely drained before putting on to the filling machine.

STAGE - VI: CHECK WEIGHING
Explanation:
(a)     Weigh all filled cylinders coming out of the carousel, (i.e. ensure 100% check weighing)
(b)     Check-weighing is performed to verify that the cylinder has been filled correctly within the permissible limits. This check is very important from safety point of view.
(c)      The permissible limit of variation is  2% of the specific weight of the product to be filled in the cylinder. Accordingly, for the quantity of 15 kg of LPG, the cylinder would be termed under-filled if the product weight is less than 14.7 kg and it would be termed as over-filled if the product weight is more than 15.3 kg.
(d)    All the cylinder coming out from the filling machines must be check-weighed to ensure 100% checks.
(e)     In case of change of composition of LPG to be filled in cylinder, the correct safe weight of the product that can be filled will to be worked out.
(f)       Over-filling, if not detected, subjects cylinders to very high pressure (due to increase in ambient temperature, liquid in the cylinder would expand and hydrostatic pressure developed may at times burst the cylinder): The danger point is reached when liquid expands to occupy fully the volumetric capacity of the cylinder, leaving no space. Once this point is reached there would be pressure rise at the rate of 24 kg/cm2 for every 1C rise in temperature. It may be noted that max. working pressure for a LPG cylinder  is 16.9 Kg/cm2 (1.66 Mega Pascal), Hydraulic Test pressure is 25.35 Kg/cm2 (2.45MPa), normal working pressure is approx. 7Kg/cm2 & burst pressure is approx 100 kg/cm2.
(g)     Likewise, under-filling, if undetected, shakes consumer's confidence.
(h)     In case any cylinder is heavily covered with mud, the same may result in under-filling when the method of overall filling is followed. It is, therefore, necessary that such cylinders are washed before filling. Particular care should be exercised to inspect the joint between foot ring and dished ends of the cylinder as there is greater possibility of accumulation of mud there.
(info)        Over-filled cylinder must be sent for immediate evacuation of excess quantity.
(j)       Each filling machine should be allotted serial no. at the Plant. Periodically, this number should be marked on the cylinder under filling on respective machine. When these cylinders are checked on the check-scales, record of actual observations should be made. This process helps to identify a filling machine giving incorrect filling.
(k)     Check-scales should be certified by the Weights and Measures Department, and must be tested against standard weights at least once during the shift.
STAGE - VII: SEGREGATION - II
Explanation:
(a)     Cylinders rejected at check-weighing are segregated as below:
i. Overfilled cylinders are segregated and sent to evacuation unit for removing excess    quantity.
ii. Under-filled cylinders are segregated and sent for topping up on a separate stationary weighing scale having a filling point.
(b) Cylinders having apparent leaks should also be segregated at this stage and corrective   action taken to stop the leak. If leak cannot be stopped, the cylinders should be sent for evacuation.

STAGE - VIII: TIGHTNESS TEST - I
Explanation:
(a)     'SC' type valve
In case of 'SC' type valve the valve seat remains in closed position unless pressure is applied against the spring. With the valve outlet open, any bubbles emerging out through the valve outlet would indicate leak through the valve seat.
(b) General
i. At this stage, leakage through bung or cylinder body may also be noticed in the form of    bubbles emerging out from the leaky spot.
ii. In case of any leak of above nature the cylinder is marked for segregation with appropriate marker to identify the type of leakage.
(c) The tightness tests are intended to check leak through the cylinders which could be through:
i. Cylinder's parent metal or pin hole in weld joint.
ii. Cylinder/valve joint commonly known as bung-joint.
iii. The valve seat (with valve closed).
iv. The valve spindle (with valve closed or open).
v. The valve body (very rare occurrence)
vi. The special adaptor/valve-outlet joint (in case of 'SC' type valve).
(d) The tightness test-I is basically intended to check leaks past the valve seat.
(e)     Carousel type of tightness testing baths, which keep the cylinders in vertical position, are ideally suited for checks at this stage.
(f)     Painting of interior surface of the test bath with white paint, provision of sufficient lighting arrangement and periodic changing of water for the test to ensure that it is clean, help in easy detection of the leaks.
(g)       Whenever leak is observed, attempts should be made to stop it, if possible (e.g. by tight closure of 'F' type valve or fixing of security nut/cap etc.)
(h)       If the leak cannot be stopped the cylinder should be sent for evacuation.
(info)      Suitable markers should be used to identify type of leaks such as valve leak, bung leak, etc.
(j)       The leaky cylinder, before it could be evacuated, should be so placed that the leakage is that of vapor and not liquid.
STAGE - IX: SEGREGATION - III
Explanation
(a)     Leaky cylinders from tightness test bath-I should be segregated and sent to Evacuation Unit.
STAGE - X: PREPARING CYLINDER FOR TIGHTNESS TEST - II
Explanation:
(a)     Cylinder with 'SC' type valve
i. Water to be blown from the cavity of the valve, by air. (The cavity may be full of water              when the cylinder comes out from the test bath - I)
ii. Special type of adaptor (dummy pressure regulator) to be fixed, locked and adjusted on the valve. After fixing the adaptor, the knob is to be turned in on position to keep the valve seat open. The adaptor is basically a body of Pressure Regulator with diaphragm and related parts removed and outlet blocked (i.e. dummy Pressure Regulator). Alternatively  the effectiveness of the 'O'-ring can also be checked through portable leak-detector  which could be mounted on the cylinder valve, and leak, if any, observed through the   fluid in the detector.
STAGE - X: TIGHTNESS TEST - II
Explanation:
(a) 'SC' type valve
i. With the valve seat in open position with the help of special adapter the effectiveness of    the 'O' ring (making a joint with the inlet of the pressure regulator) is tested.
(b)     General
i. Tightness test is carried out with the valve seat in open position and outlet closed, with security nut in case of 'F' type valve and with adaptor in case of 'SC' type valve.
ii. At this stage leakages through bung or cylinder body are also checked which may be noticed in the form of bubbles emerging out from the leaky spot.
(c)     Leakage past valve seat having checked at tightness test bath I (STAGE - VII), other possible leaks are tested through tightness test bath II.
(d)     Suitable markers should be used to identify types of leaks such as bung leak, valve leak etc.
(e)     Immediate action should be taken to stop the leak temporarily wherever practicable. If the leak cannot be stopped, the cylinder should be sent for evacuation and should receive priority over defective cylinders which are not leaking.
(f)       The leaky cylinder, before it could be evacuated, should be so placed that the leakage is that of vapor and not liquid.

STAGE - XI: SOAP SOLUTION TEST
Explanation:
(a)     Soap solution test is applied to check bung leaks in case of both 'F' type and 'SC' type cylinders. This is in addition to the two tightness tests carried out at stage VIII and Stage XI. A suitable marker should be placed to identify bung leak.
(b)     White applying soap solution to the bung/valve joint it must be ensured that the solution is applied all around the valve/bung joint.
(c)     Soap only should be used for making a soap solution and not a detergent.
(d)     Soap solution test is done to detect minute leaks through the joint which normally remain un-detected in water baths.
STAGE - XII: SEGREGATION - IV
Explanation:
(a) Leaky cylinders from tightness test-II should be segregated and sent to Evacuation Unit.
STAGE - XIV: FINISHING OPERATIONS
(b) Cylinders with 'Self-Closing' valve
i. Remove special adaptor (if fixed).
ii. Blow cavity of the valve outlet with air in case any water is observed.
iii. Fix the security cap on the valve outlet.
iv. Fix appropriate neck label.
v. Seal the valve outlet using sealing tape.
STAGE - XIII: FINAL INSPECTION
Explanation:
(a)     Check the cylinder visually for:-
i. Apparent sound condition.
ii. Presence of cap, and neck label in case of cylinders with 'cap' as valve protection.
(b)     Correct deficiency noticed, if any.
STAGE -XIV: DISPOSAL OF FILLED CYLINDERS IN SOUND CONDITION.
Explanation:
(a)     At this stage the cylinders are ready for delivery:-
i. If required the fit cylinders can be directly sent to the stake trucks for loading.
ii. If no stake-truck is available, the cylinders can be sent for stacking in the area earmarked for the purpose.