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TECHNOLOGY - TANK CLEANING essentially, using a cleaning chemical at a dilution rate of 10% in water will not necessarily make it 10 times more effective than using the same cleaning chemical at a dilution rate of 1%, and this is extremely important to consider. Having looked at the basic make-up of cleaning chemicals, it should also be considered that different cleaning chemicals do contain other active ingredients designed to make the materials more effective at cleaning specific residues. Most commonly these ingredients fall into three main categories: 1) Alkaline based. Primarily for the purpose of saponification of vegetable oil based residues. 2) Acid based. Primarily for removing more stubborn residues that do not readily dissolve in water, but become more soluble in acids, for example hardness salts and other surface contamination that otherwise render the appearance of the cargo tank as ‘dull’ or ‘not typical’. 3) Organic solvents for the purpose of ‘cutting’ heavy hydrocarbon residues. Indeed, many cleaning chemicals that are sold into the domestic market for various applications are based on the same formulations, but that is where the similarity ends. The method of operation for domestic cleaning chemicals is completely different to the cleaning of chemical and product tankers and this raises a question, relating to the cleaning chemicals used on board tankers being ‘fit for purpose’ and whether or not any studies have actually been carried out by the cleaning chemical manufacturers to determine this. Domestic cleaning chemicals tend to be used on floors (horizontal surfaces) and walls (vertical surfaces), both of which are readily accessible and can therefore be manually scrubbed or brushed. Other surfaces or areas that need cleaning (including clothing) can usually be soaked in a solution of the cleaning chemical for any given period of time and it has to be accepted that soaking is probably the most effective way of cleaning any material or surface because there is intimate and prolonged contact with the cleaning material. But of course on a tanker, it is just not feasible to ‘soak’ the inside of a cargo tank with a cleaning material. Inefficient method Furthermore, when one considers the way in which a cargo tank is cleaned, it soon becomes apparent that this method is actually quite inefficient. The aqueous solution of the cleaning material is sprayed over as many points of the tank as possible, usually via the rotating nozzle of a tank cleaning machine, which really only allows the cleaning material merely to run down the surface of the bulkhead, with an extremely short contact time. Prolonged cleaning will of course increase the contact time of the cleaning material on the bulkhead, and this is really the only viable option for enhancing the efficiency of the cleaning operation, but when a vessel has a number of cargo tanks to clean simultaneously, time is not always available. Consider one more point, vessels that are cleaning to a very high purity standard (for example prior to loading chemical cargoes), very often have to pass a methanol wall wash inspection prior to loading. For coated cargo tanks, the wall wash test is not just a measure of how clean the surfaces of the tanks are, it is also a measure of the amount of absorbed/ adsorbed residues that the wall wash solvent (usually methanol) is able to chemically extract from the outer layers of the coating. Organic coatings readily absorb and retain low carbon chain molecules, for example lower alcohols, some aromatics, ketones, chlorinated solvents etc. and it is known that these products will stay inside the coating, until they are actively removed, either by tank cleaning methods or by extraction into a subsequent cargo. The degree to which they can be removed is largely influenced by their volatility. Inorganic (zinc silicate) coatings absorb the same types of cargoes, but because of the open/porous nature of the coating surface, these cargoes are generally not retained. However, due to their inherent porosity and their fairly rough surface profile, previous cargo residues may become absorbed and/or adsorbed into the coated surface and as a result some cargo residues may be retained, including non volatile and ‘oil-like’ cargoes. These must be actively removed either by tank cleaning or by extraction into another cargo, otherwise they could pose a contamination threat to subsequently loaded sensitive chemical cargoes. In other words, if a cleaning chemical claims to be able to remove previous cargo residues to a standard where a wall wash inspection will be accepted, (in the case of cleaning coated cargo tanks) this actually means that the cleaning chemical must have the ability to penetrate inside the coating and remove traces of previous cargoes that may be residing there. This is an extremely bold claim to make, particularly as the industry is rapidly moving away from the use of solvents as cleaning materials for coated cargo tanks (for safety reasons), even though solvents are still proven to be the most effective way of removing absorbed/adsorbed residues from within cargo tank coatings. Clearly the challenge is to find surface active cleaning materials that can clean coated cargo tanks to a wall wash standard, before the use of tank cleaning solvents is prohibited, otherwise owner and charterers of chemical and product tankers will be facing serious tank cleaning headaches in the future. All of this being said, whether the cleaning chemicals are for cleaning stainless steel or coated cargo tanks, for general use or for achieving a high purity standard, they should still be effective (particularly in view of the significant volumes that are used on board tankers today). As noted, there seems to have been no evaluation of this type in the past, with the efficiency of most cleaning chemicals seemingly based on the ability of the chemical to visually remove previous cargo residues during the tank cleaning process. However, as noted with more vessels now being inspected to a chemically clean standard (by means of a wall wash inspection), it is really no longer acceptable for cargo tanks to be merely visually clean prior to loading many chemical cargoes and with this in mind, L&I Maritime (UK) Ltd (LIM) was asked by a major chemical tanker owner to investigate this issue in more detail. Procedure One of the reasons why monitoring the efficiency of tank cleaning chemicals does not appear to have been carried out in the past, could be because there is no official or immediately straightforward procedure to do so. The procedure adopted for this project was standardised as far as possible in order that the results generated could be reproduced as long as the test panels were treated in the same way. But as noted, the procedure is not an industry standard. There are many different causes of cargo tank contamination and as noted, many different types of tank cleaning chemicals available to remove the contamination. However, for the purpose of this project, one particular situation/scenario was chosen and that was cleaning zinc silicate coated test panels after exposure to Linear Alkyl Benzene (LAB), which is a known persistent hydrocarbon. It is known that zinc silicate coatings actively retain hydrocarbon based, non volatiles and it also accepted that one of the most common generic types of tank cleaning chemical is the ‘hydrocarbon remover’ so bearing these two points in mind, it made sense to base the project around this particular scenario. 28 TANKER<strong>Operator</strong> November/December 2009
TECHNOLOGY - TANK CLEANING It was also considered that cleaning persistent hydrocarbons from zinc silicate is one of the most challenging operations facing chemical/product tanker owners and operators so it could be assumed that the tank cleaning chemicals that performed the best under the conditions of the project, would most likely be some of the most effective in the market place. The efficiency of each tank cleaning chemical was monitored by means of wall washing the test panel with a fixed volume of methanol. This methanol was then tested for water miscibility (hydrocarbons) in accordance with ASTM D1722, but rather than just visually ‘passing’ 20 or ‘failing’ the sample (as stated in the ASTM procedure) the extent of the hydrocarbon failure was quantified using the L&I WAVE II UV / Vis Spectrometer. The following test protocol was agreed: 1) Three zinc silicate coated test panels were fully immersed in Linear Alkyl Benzene (LAB) for 48 hours. 2) The panels were removed from the LAB, flushed with cold freshwater for approximately 1 minute (in order to remove the free LAB from the surface of the test panels) and then naturally ventilated to dryness. 3) The panels were then washed by recirculation using the tank cleaning chemical (at the concentration specified by the manufacturers) for 2 hours at 60 deg C in fresh water. 4) The panels were again flushed with cold freshwater to remove any residual detergent and then naturally ventilated to dryness. 5) Each panel was then wall washed with methanol and tested for hydrocarbons using the LIM spectrometer to quantify the hydrocarbon content of the sample. The reported result was an average of all three results. It was agreed to limit the cleaning water temperature to 60 deg C, because this temperature is considered to be the lowest ‘hot’ water temperature that can be readily achieved and maintained by most chemical/product tankers. The cleaning was carried out using a tank cleaning rig that LIM has made specifically for the purpose of replicating the tank cleaning action on board chemical/product tankers. The test panels were sprayed with the cleaning chemical solution, in a similar manner to the way the bulkheads of a cargo tank would be sprayed. In order to create a control (reference) for the project, the zinc silicate coated panels were initially treated in the same way as above, apart from the fact that no cleaning chemicals were added in part 3. It was expected that the cleaning effect on the test panels without using tank cleaning chemicals would be minimal and when the panels were wall washed the results would show the highest residual hydrocarbon readings. At the same time, when the panels were cleaned with the individual tank cleaning chemical solutions, the hydrocarbon readings from the wall wash samples would be expected to be significantly better. The most efficient cleaning chemical solutions would therefore be expected to show the lowest hydrocarbon readings. Cleaning chemicals from seven different THE DIFFERENCE IS OBVIOUS. SO ARE WE. OPERATIONS WITH A DIFFERENCE. EMIRATES ENVIRONMENTAL PROTECTION Co. L.L.C. A MARPOL Reception Facility in the Port of Khorfakkan, U A E Tank Cleaning/De-mucking, De-slopping, Treatment & Disposal of Oily Sludge, Slop & other petroleum waste. P.O.Box 43729, Dubai, U.A.E. Tel : +9714 397 2277, Fax : +9714 397 9212 Email: eco@emirates.net.ae Website: www.ecouae.com November/December 2009 TANKER<strong>Operator</strong> 29
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Page 3 and 4: Contents 04 06 10 Markets Valuing a
Page 5 and 6: Intershield ® 300 Abrasion resista
Page 7 and 8: INDUSTRY - MARKETS Income Approach
Page 9 and 10: INDUSTRY - INTERTANKO PROFILE Inter
Page 11 and 12: Think local. Act global. Hilanders
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Page 15 and 16: INDUSTRY - GIBRALTAR REPORT “In t
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Page 21 and 22: INDUSTRY - GIBRALTAR REPORT technic
Page 23 and 24: INDUSTRY - BUNKERS Increase in high
Page 25 and 26: INDUSTRY - BUNKERS Low sulphur mari
Page 27 and 28: INDUSTRY - BUNKERS Maximising effic
Page 29: TECHNOLOGY - TANK CLEANING How effi
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Page 35 and 36: TECHNOLOGY - EMISSIONS regulators f
Page 37 and 38: TECHNOLOGY - EMISSIONS closed gaugi
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Page 41 and 42: TECHNOLOGY - EMISSIONS Allweiler pu
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Page 45 and 46: TECHNOLOGY - NAVAIDS Electronic pas
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Page 50 and 51: TECHNOLOGY - SHIP DESCRIPTION Enhan
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