Development of an automatic gas cylinder alignment device ...

การประชุมวชิาการระดบัชาต ิครัง้ที ่1 มหาวทิยาลยัเกษตรศาสตร ์วทิยาเขตศรรีาชา ประจ าปี 2559

________________________ 1 Integrated Design and Manufacturing Systems Research Unit, Faculty of Engineering at Sriracha, Kasetsart University Sriracha Campus, Chonburi 20230, Thailand. *Corresponding author: E-mail [email protected]

Development of an automatic gas cylinder alignment device for LPG bottling process

Nachon Sathonsaowapak1 and Thittikorn Phattanaphibul1*

ABSTRACT

Liquefied petroleum gas (LPG) is the main fuel for cooking in many countries. In Thailand, the annual consumption of LPG used by households has grown continuously. Presented in this paper is a case study of an LPG company that must increase the productivity by 26% to support this higher market demand in Eastern region of Thailand. Therefore, quality control (QC) story approach was applied to determine tentative solutions for gas bottling process improvement. Results illustrated motion and waiting waste occurred in process that had led to the development of an automatic gas cylinder alignment device (AGCAD). After testing and implementation, the cycle time was reduced to 4.1 seconds per cylinder and the productivity could be increased by 29.5%. Keywords: LPG, Productivity, Improvement, Gas Cylinder, Automatic

INTRODUCTION

Liquefied petroleum gas (LPG) is a hydro-carbon product, typically consisting of propane (C3H8) or butane (C4H10) or propane-butane mixture. LPG is a flammable gas that has high heating value. Thus, LPG is widely used as fuels in many applications, e.g., cooking, transportation, manufacturing, and power generation. Besides, LPG is used as a feedstock in upstream petrochemical industry to produce ethylene also (Jarurungsipong and Rakthum, 2012), (Falkiner, 2003). In Thailand, the demand of LPG could be classified by end-user including: (1) household, (2) industry, (3) transportation, (4) petrochemical industry (as feedstock and fuel). Fig. 1 illustrates the annual LPG consumption on each segment that has grown continuously due to economic expansion (EPPO, 2013).

Fig. 1 LPG consumption rate. (EPPO, 2013)

In order to support the demand of the household segment that is the largest share of the total demand, an LPG company aimed to increase the productivity by 26% to maintain the market share in the Eastern region. Thus, a quality control (QC) story approach was applied to explore tentative solutions for improving gas bottling process (JUSE, 2001). Research methodology is presented in the next section which

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includes the details of case study, QC story and concept development of the device to increase the productivity. Conclusion is provided at the last section.

METHODOLOGY

Current productivity of the studied LPG company

Typically, Thai LPG companies distribute LPG to the household users via four standard cylinders’ size of 4, 7, 15 and 48 kg. For the Eastern region, the 15-kg size had the largest demand. The studied LPG company was one of the main LPG providers. Fig.2 shows the current productivity of 1,802 cylinders per day on average (62% of the total productivity).

Fig. 2 LPG productivity by cylinders’ size

LPG bottling Plant

The LPG bottling plant includes eight activities as the followings: (a) receiving empty cylinders from LPG retailers, (b) screening out the minor damaged cylinders to repair (e.g., replace defective valve and/or handle, repaint cylinders’ surface with identification mark and brand); however, the cylinders may be disposed in case of having severe defects, (c) cleaning outer surfaces of the qualified cylinders to remove dirt, (d) bottling LPG into the cylinders (LPG is delivered to the company via rail tank wagons and bullet tank trucks; and transferred to the storage tank before bottling process), (e) checking weight of all filled

cylinders, (f) testing the cylinders for leak, (g) fixing a tamper-proof seal at each cylinder’s valve, and (h) delivery the filled cylinders to the LPG retailers. In addition, the chain conveyor unit was used for moving the empty and filled LPG cylinders from one location to another location within the plant, excluding the LPG bottling carousel that had its own material handling unit. Fig. 3 illustrates summary of all activities, (a) – (h).

Bottleneck in LPG bottling process

Excluding (a), (b) and (h) that were changeable activities of the production process, the remaining five activities, (c) – (g), were checked for their operation times as shown in Table 1. The highest operation time indicated the bottleneck of the process. As a result, the LPG bottling process should be improved in order to increase the productivity. At LPG bottling carousel, there are six sub-operations as the followings: (d1) connecting the LPG bottling nozzle to the cylinder’s valve, (d2) keying in process parameters, (d3) pushing start button, (d4) bottling LPG into the cylinder, (d5) shutting off the cylinder’s valve, and (d6) disconnecting the LPG bottling nozzle from the cylinder’s valve.

Table 1 Operation time in the LPG bottling plant

Activity Operation time

(seconds/cylinder)

(a) receiving the empty cylinders -

(b) screening out the damaged cylinders -

(c) cleaning the used cylinders 3.0

(d) bottling the LPG into the cylinders 5.7

(e) checking weight of the filled cylinders 2.5

(f) testing the cylinders for leakage 4.4

(g) fixing a tamper-proof seal 3.0

(h) delivery the cylinders to the retailers -

48 kg; 13%

4 kg, 20%

7 kg, 5%15 kg, 62%

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Fig. 3 Activities in the LPG bottling plant

Identifying a root cause

A cause-and-effect diagram was created as shown in Fig. 4. Results illustrated possible causes of the bottleneck resulted from material, method, machine and man. By brainstorming, the root cause should be the material handling unit of the LPG bottling carousel that could not control the orientation of the cylinder. Normally, an in-charge operator must connect the LPG bottling nozzle to the cylinder’s valve while the material handling unit was still running (the current rotating speed: 73.8 seconds per round / the LPG bottling time: 60.6 seconds per cylinder). Fig. 5 shows the layout of LPG bottling carousel that consists of the material handling unit and the LPG bottling nozzles. In case that the cylinder’s valve was not aligned properly as shown

in Fig. 6(a), the operator must rotate the cylinder manually until the the LPG bottling nozzle could connect to the cylinder’s valve as shown in Fig. 6(b). Fig. 6(c) shows the top view of the possible space where the cylinder’s valve can be connected with the LPG bottling nozzle. This additional operation, rotating the cylinder, was always appeared in process that resulted in fatigue of the operator and longer operation time (3 seconds per cylinder on average used in connecting the LPG bottling nozzle). In addition, the waiting time at the end of the process might be required to accomplish bottling operation due to delay start. For worst-case scenario that the operator could not handle the process, the entire production line must be stopped suddenly.

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Fig. 4 Cause-and-effect diagram for the bottleneck in the LPG bottling process

Fig. 5 Layout of the LPG bottling carousel

Fig. 6 Alignment between the cylinder’s valve and the LPG bottling nozzle

(a) improper characteristic, (b) proper characteristic, (c) possible space

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RESULTS AND DISCUSSION

Concept Development of an AGCAD

In order to increase the productivity, the occurred motion and waiting wastes must be eliminated. A possible solution is to develop a mechanism to provide proper alignment between the cylinder’s valve and the LPG bottling nozzle. A simple principle of wheel that rolls onto the ground might be applied to provide self-alignment function of the LPG cylinder. Normally, the wheel needs a certain amount of friction so that the point of contact between wheel and ground will not slip. Fig. 7 illustrates the free body diagram of the rolling wheel.

Fig. 7 Free body diagram of the rolling wheel

Therefore, automatic gas cylinder alignment device (AGCAD) has been designed as shown in Fig. 8. A main conceptual design was to make it as a modular unit that could be operated with the current process, rather than modifying the hardware, to avoid process disturbance.

Construction of the AGCAD

Fig. 9 presents the constructed AGCAD. The device consists of (1) a rotating unit, (2) a friction plate, (3) an orientation locking unit: (3.1) six L-shape plates with rollers, (3.2) six double-acting pneumatic cylinders, (3.3) six 5/2 way-roller-lever pneumatic valves, (3.4) a spring plate, and (4) a power transmission unit.

The rotating unit included two hexagonal-star plates (top and bottom plate) that were driven by the power transmission unit. It cooperated with the friction plate to make the LPG cylinder rolled forward until the cylinder’s valve reaches the set direction.

The friction plate was fixed on the side of the chain conveyor unit as well as the rotating unit was placed on the other side. The friction plate was used to stop slipping motion of the LPG cylinder at the contacted side while the opposite side was being pushed by the rotating unit. As a result, the LPG cylinder started rolling forward.

The orientation locking unit played an important role to control the direction the cylinder’s valve. This unit, including six sub-component sets, only (3.1) and (3.2), was on the top plate of the rotating unit. The L-shape plate with roller was attached to the piston rod of the pneumatic cylinder to perform as locker for stopping the rolling motion. The piston rod was suddenly retracted when the LPG cylinder departed from AGCAD. The roller-lever of each pneumatic valve (3.3) fixed below the bottom plate of the rotating unit was pressed by the spring plate (3.4) one by one at the exit of AGCAD to activate the retract motion.

Fig. 8 CAD models of AGCAD

Driving direction

Rolling direction

Friction Force

Point of contact

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Fig. 9 AGCAD

Fig. 10 Steps of the alignment and all key components of AGCAD

Capability Testing

A preliminary study was conducted to investigate the capability of AGCAD including reliability and average operation time used in LPG bottling process. Thirty empty LPG cylinders with random orientation were fed through AGCAD. Fig. 10 shows the steps of the alignment and all key components of AGCAD. Results illustrated good reliability that all LPG cylinders were in proper orientation as shown in Figure 6(b). The operator could connect the LPG bottling nozzle to the cylinder’s valve with less time. As a result, the average operation time of the LPG bottling process was reduced to 4.1 seconds per cylinder.

CONCLUSIONS

In order to accomplish the target productivity for higher market demand, the LPG company applied the QC story approach to determine the root cause that limited the current productivity and also generate tentative solutions for improvement. Results indicated that the bottleneck was appeared in LPG bottling process due to the motion and waiting wastes. The in-charge operator often adjusted the LPG cylinders before gas bottling process on the LPG bottling carousel. The motion waste also caused waiting waste due to delay of the gas bottling process and shutting down of the production line. Therefore, an additional device named AGCAD was developed

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to have a self-alignment function to adjust the orientation of LPG cylinder that could eliminate these wastes. The testing results illustrated good reliability of the device and lower gas bottling time of 4.1 seconds per cylinder. As a result, the cycle time could be lowered to 4.4 seconds per cylinder that was the operation time of leakage testing. The productivity was improved to 2,334 cylinders per day (29.5% increase).

ACKNOWLEDGEMENTS

The authors would like to express sincere thanks to the case study company for assistance and recommendations on this study.

LITERATURE CITED

Energy Policy and Planning Office (EPPO), “Energy Statistics of Thailand 2013”, Ministry of Energy: Bangkok, Thailand, 2013. Falkiner, R.J. “Liquefied Petroleum Gas”, In: G.E. Totten (Ed.) “Fuels and Lubricants Handbook: Technology, Properties, Performance, and Testing”, West Conshohocken, Pa.: ASTM International. 2003. Japanese Union of Scientists and Engineers (JUSE), “Fundamentals of QC Circle”, QC Circle Headquarter, Tokyo, Japan, 2001. Jarurungsipong, R. and Rakthum, N. “Price Controls Support LPG Fuel Consumption”, Industry Research LPG Wholesaler, TRIS Rating, 2012.

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Development of an automatic gas cylinder alignment device ...

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