Abstract

Mini Production Suction Dredge (MPSD) has been made for people of Bangka Belitung Province Indonesia as a cheap, safe and simple technology ship to mine tin sand from surface land under sea level. This MPSD creates more safe production operation since previous ships using traditional small boat for catching fish. The main reason why this MPSD created is that there is no dive activity for operator to drive flexible suction pipe under the sea which in some cases make divers have problems and get serious injured or dead.

The MPSD is a welded construction 4 x 10 meters ship equipped with suction unit, 24 HP diesel engines to drive 2 suction pumps, tin separation jig and steering winch. The basic construction of dredge is consisting of 2 sides of 0.8 meter diameters x 10 meters steel pontoon. It operates on sea waves which takes sand up to 15 meters deep from mean sea level and allows no diving activity in 1 mile away from coast line. Through its operation, the MPDS operated more stable and safer than previous operation.

Keywords: tin dredge, suction, safe operation

I. INTRODUCTION

Tin is one of important material used in electronic industries, automotive and other industries. Tin producer in the world comes from several countries like China, Bolivia, Australia, Malaysia, Nigeria, Thailand, Zaire and Indonesia. Through tin companies operated in Bangka Island Indonesia like PT.Timah Tbk and PT. Koba Tin, Indonesia has capacity to produce at least 60.000 Ton of tin each year. Compare with other tin producer countries, Indonesia produce the highest amount of tin Bangka Belitung Island is a small island in South East Sumatra. It becomes the 31st Province in Indonesia in the year of 2000. Bangka Island is the biggest tin producer. Its geographical location is strategic since it located in economy-triangle

Singapore-Johor-Riau closed to Batam Island which is ASEAN gateway from Indonesia, and Natuna Island which is the biggest natural gas resources in Indonesia. Bangka Island is located in 10450 - 10930 East Longitude and 050 - 410 South Diagonal and has warm climate between 25 - 26C.

II. TIN MINING TECHNIQUES

The mining techniques to produce tin sand from land surface or alluvial are using water gun with gravel pumps. Water is pumped to land surface and through elevated surface it goes to the sluice box equipped with riffle to catch the feed (mud mixed with many kinds of materials including tin sand). After hours of that such operation, people then stir up the feed with hoes makes the tin sand stand in sluice box and other materials are expelled with water flows since they are lighter than tin sand. Fig.1 illustrates the working principle of gravel pump mining. Meanwhile on the Bucket Dredge, Fig.2 illustrates it, which is operated on the sea level; tin sand is produced by digging land surface under sea level by means of buckets. Buckets bring the feed up to washers through screen as to separate sand from stones. The feed goes to jigs which catch the tin sand with a principle of specific-weight different basis. The jig is an open tank completed with flat screen and iron hematite in small grain size on it. Under the tank, there is diaphragm full of water which moves up and down by means of eccentric rotation driven by electric motor. This motion creates blow up and suction of water. Therefore, there is a minerals separation process of feed because of its specific-weight and tin sand stays on jig. Fig.3 shows jig working principle. Both in land or sea, the process of getting tin sand has the same principle.

Beside Bucket Dredge, there is Cutter Suction Dredge to open the line of Bucket Dredge operations. The capability of this dredge is to remove land, sand or mud surface under sea level to other places through pipe lines. Cutter is used to stir up the land and then sucked by gravel pump through suction pipe in the ladder. Since the end of 1970 era, higher capacity of Cutter Suction Dredge has been used to peel and to remove overburden the land surface under the sea. Fig.4 illustrates it.

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Fig. 1. Working principle of tin land mining using gravel pump ( taken from S. Sujitno, Sejarah Penambangan Timah di Indonesia, Abad 18 Abad 20., page 56, Cempaka Publishing., Jakarta, 2007)

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Fig. 2 Bucket dredge ( taken from S. Sujitno, Sejarah Penambangan Timah di Indonesia, Abad 18 Abad 20., page 78, Cempaka Publishing., Jakarta, 2007)

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This kind of sea tin mining technique is valid until now and conducted by tin mining companies. Reference [1] was said that in early August 1997, Asian monetary crisis has bad impact to Indonesian economy situation and reach its peaks in 1998. In 1999 Indonesian government established the regional autonomy institution which gave new format to local government and it takes place of local government to the reformation era. In 2000, Bangka Belitung became new province and facing new problems. The fall of pepper price, as one of main higher income to Bangka Island society and better price of tin products, US $7000/ton, pushed people to have wild tin mining as their best way to surpass the economy crisis. Only a year after, 8000 unconventional mining in small scale tin mining, spots appear. Nowadays, they can do it legally after fulfill and obey the local government rules.

People, who conduct small scale tin mining in the sea, use a simple technique to get tin sand. Using 24 HP fish boat, it is equipped with one 22 HP diesel engine to drive 4 inch suction pump. Flexible hose is used to deliver feed from land surface to 1 X 2 meter sluice box. To get alluvial from approximately 10 meters down deep sea level, someone has to dive and to keep the nose of flexible hose while he sucks the feed. The divers dive with the aids of breathing system consisting of small air pump, masker and hose to transfer fresh air from air pump to masker. Hundreds of them produce tin sand but many of them get injured or died because of accident.

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Fig.3 Working principle of jig ( taken from S. Sujitno, Sejarah Penambangan Timah di Indonesia, Abad 18 Abad 20., page 58, Cempaka Publishing., Jakarta, 2007)

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Fig. 4 Cutter suction dredge ( taken from S. Sujitno, Sejarah Penambangan Timah di Indonesia, Abad 18 Abad 20., page 95, Cempaka Publishing., Jakarta, 2007)

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III. MINI PRODUCTION SUCTION DREDGE

A. Design Considerations

Facing many problems regarding small scale tin mining in the sea, makes local government, university and tin companies have to do something to fix those problems. The solution is not only in technical aspects but also in environmental and economical aspects. The last two aspects, i.e; environmental and economical aspects have been discussed and the results are directed to legal area of mining, which concerned to environmental issues and safety mining process in the sea. Meanwhile, in economical aspect, Mini Production Suction Dredge (MPSD) will be sold to people through a credit system paid by tin sand and sell it to tin company as the producer of this MPSD.

The design of MPSD should be paid attention to:

1. ) The dredge should be made from medium-strong material which withstand to 1-2 meters sea waves and can operates approximately 3 years with minimum maintenance.
2. ) It operates without divers since there are many accidents happened in previous operations.
3. ) It should be easy and safe operated.
4. ) Not necessarily equipped with propeller driven engine since it will be pulled with small boat or fish boat. Its operation is not exceeded 1 mile from coastal area.
5. ) The process of mining uses suction system and sluice box to wash the feeds.
6. ) It has its drive system to self positioned in the certain surrounding area of production.

Discussion has been made to appear many options of the design of MPSD through PT.Timah and local government. The design then approved to be manufactured. Fig.5 shows the design of MPSD.

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Fig. 5 The design of MPSD

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B. Structure of MPSD and Its Working Principles

The main structure of MPSD is consisting of 5 unit i.e;

1. Pontoon System and Dredge Construction
2. Weighted Suction System
3. Suction Pumps System
4. Feed Wash System
5. Drive Winch System

Those 5 main structures of MPSD will be explained as follows:

1. ) Pontoon System and Dredge Construction: consist of 2 pontoons with dimension 0.8 m diameter X 10 m long, side by side with maximum 4 m width. Constructed with weld joint, the pontoons are united with dredge construction. Using 100 mm U profile of steel, 2 inches diameters of pipe the dredge presents the floor, canopy and fences. Fig.6 illustrates its pontoon and dredge construction.
2. ) Weighted Suction System: this system consists of weighted suction pipe, drive system to control deep position of weighted suction pipe. Using 100 mm U profile of steel, 2 and 4 inches diameters of pipes, winch system, 0.5 inches of steel rope. The weighted suction pipe is used to make sure the nose of suction pipe will go down and touch the land surfaces. Beside, if the MPSD waved because of sea waves, this tool can stir up the feed before sucked up. Fig.7 illustrates weighted suction system.
3. ) Suction Pumps System: the system is equipped with 24 HP diesel engines which drives 1 gravel pump, 1 self-priming pump. 15 m long flexible hose with 4 inches diameter is used to transfer the feed from weighted suction pipe to sluice box. From gravel pump to sluice box, MPSD used 4 inches PVC pipes. Fig.8 illustrates it.
4. ) Feed Wash System: this is a sluice box made from hard wood plates. There are 3 kinds of boxes to have 3 steps of processes. First step is to receive feeds from ends of 4 inches PVC pipe. High speed of feeds velocity comes from it makes this box prevent from splashing out of feeds and directed it to the second box. The second and third box have the same function to let the feeds flows and tin sand will stay there while other lighter material flows together with water flows. These boxes have 3-4 Degrees declined position to horizontal line.
   
   
   

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   Fig.6 The basic dredge construction.
   

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   Fig.7 The weighted suction system.
   

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   Fig. 9 illustrates feed wash system.
5. ) Drive Winch System: This system allows MPSD moves right and left side on the rear dredge, while the MPSD is tightened by anchor approximately 10 m by means of plastic rope to the front side of MPSD. To moves MPSD, winch system used to pull plastic rope to the side; meanwhile it lets rope to other side by rotating the steering winch. Fig.10 illustrates the drive winch system. Fig. 11 and Fig. 12, shows the real MPSD and its operation.

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Fig.8 Suction Pumps system

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Fig.9 Feed wash system

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Fig.10 The drive winch system

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Fig.11 MPSD build in Air Kantung;s dock

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Fig.12 MPSD in action

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IV. CONCLUSION

The MPSD is made as a combination of Bucket Dredge, Cutter Suction Dredge and Sluice Box in design and working principles. Pay attention to work safety issue, economy and simple technology use this dredge has an important role in creating middle technology for better life of people in Bangka Belitung Island. Operated by 2 operators, MPSD makes operation efficient and safe since no one of them needs to dive into the deep sea.

The MPSD now operated in the sea and will mass produce to change the previous system which has many serious problems. With the aid of simple technology, MPSD exactly implement the effective and easy to operate. Based on the experiment, this dredge can be improved by adding propeller which connected to diesel engine through coupling and with steering system, this MPSD can move by its own power.

ACKNOWLEDGMENT

The making of MPSD is successful and satisfies all parties in small scale tin mining in the sea. In this opportunity, let the authors thanks to the following parties:

1. Prof. Dr. Bustami Rahman, MS. Rector of Bangka Belitung University (UBB).
2. Nyayu S. Chodijah, M.Si., Head of UBB Research Centre
3. Ir. Yono, M.Sc., M.M., Head of Engineering PT.Tambang Timah.

REFERENCES

[1] S. Sujitno, Sejarah Penambangan Timah di Indonesia, Abad 18 Abad 20., Cempaka Publishing., Jakarta, 2007.

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Team Research By :


Prayitnoadi R.P.
priyoko@ubb.ac.id;

Rodiawan
rodiawan@ubb.ac.id;

Purnama A.W.C.
wahyu@ubb.ac.id;

Sapjah D.
dedih@ubb.ac.id

Erafeli B.
bustari@ubb.ac.id;

Mechanical Engineering Study Program
State University of Bangka Belitung, Indonesia

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