Safe Transportation of Sulfur
Sulphur refers to five main commodities for the chemical industry. Sulphuric acid derived from sulphur is known as "bread of the chemical industry". Each year, more than 100,000 open rail cars of sulphur are transported only in Russia.
At the same time, sulphur is dangerous goods referred to hazard class 4, subclass 4.1. It is inflammable solid substance able to ignite from a match flame, spark, and burn extensively in an open rail car forming toxic oxides. Moreover, there could be rail tank cars with crude oil, petrol, hydrocarbon gases and other dangerous goods, as well as passenger and local trains nearby. The fire of sulfur violates the movement of trains, an emergency rail car has to be detached from the rolling stock and measures to extinguish the fire have to be taken.
That is why during sulphur transportation, special precautions are taken in accordance with the Agreement on International Goods Transport by Rail (SMGS) and Agreement on Special Conditions Transportation of Dangerous Goods, signed by and between JSC Russian Railways and the owner of the dangerous goods.
Special conditions of sulphur transportation developed and constantly improved. Special conditions transportation JSC Russian Railways include presence of flexible cover in the form of non-combustible tent and the complete absence of open surface of Dangerous Goods on the whole route from the consignor to the consignee.
Fig.1. The cover sulfur was damaged after the rail car travelled 1,200 km.
In spite of numerous works in Russia and abroad on the prevention of sulphur ignition in rail cars, such situations happened quite regularly, which is known from media reports. It was believed that either ignition happened because of sulphur self-ignition, or, as others may think, sulphur ignition was caused by the surface damaged of the cover resulting from thefts or attempted thefts the cover. Few registered cases of cover thefts could not explain numerous events of smoke generation in rail cars with sulphur.
Fig.2.Sulfur fire in an open rail car under the cover – the fire was focused at the rupture of joint connecting cover canvas. The rail car is shown after the flame in the fire area has been extinguished.
To prevent sulfur fire in rail cars numerous experiments have been conducted. The mechanism of structural failure of covers before the end was unclear, and was used the method of trial: increasing tensile strength of a cover fabric; redesign covers and change their sizes; using of multi-layer covers instead of single-layer one; increase strength tapes that fasten cover to the walls of the car; etc. The number of smoke generation events and sulphur fires in open rail cars has reduced.
However, in transit open rail car continued cases the damaging of cover surface and cars were removed from the railroad rolling stock in commercial point inspection rail cars. In the commercial point inspection rail cars damaged cover were not removed and new cover fastened at the top.
Researches have shown that this problem can be solved using a comprehensive systems approach. It is necessary to know the characteristics of the following factors to be taken into account: the construction of the open rail car, and primarily, the location and number of middle binding devices of the open rail car; tensile strength of the fabric cover and air permeability of fabric cover; atures of the cover construction itself; tensile strength and the number of fasten tapes (to fasten the cover to the wall of rail car); tensile strength and the number of strapping tapes; the speed of train; wind speed and direction, maximum wind speed, wind speed during gusts of one.
Monitoring of covers in open rail cars in Kazakhstan, Volga, North Caucasus, Donetsk and Odessa Railways showed the necessity to eliminate windage of covers in open rail cars. This information was also stated in telegrams sent by Railways of JSC Russian Railways to the consignor in cases of sulphur fires and sulphur surface denudation along the route. Full-scale experiments related to the use of long pieces of round-link chains as tie down devices welded vertically around the entire perimeter of rail cars were performed. Such activities made it possible to continue the work in this field.
With the priority as of August 9, 2011, NEK was granted the Eurasian Patent No. 018271 for invention “Method, arrangement and means to cover bulk cargo during rail transportation”. The core idea of the invention was to provide minimum air gap between the cover and sulphur surface, it was proposed to use numerous middle tie down devices located at different heights on the rail car wall instead of separate middle tie down devices, located around the rail car perimeter.
One of the main reasons of sulphur ignition, under certain conditions, was in underestimating of aerodynamic forces applied to the cover, which occur at high train’s speed, as well as, during strong head or crosswind.
LLP TENGIZSHEVROIL has set a task for NEK to find a technique to test a full-sized sulphur cover with sizes 12 x 3 m instead of testing a cover piece of 50 х 200 mm to select the best available cover from samples provided by numerous suppliers. To solve this problem it was decided to refer to the center of aeronautical science, TsAGI, for assistance that had the wind tunnels to test air vehicles.
Within the period of 2010−2011, Central Aerohydrodynamic Institute named after N.E. Zhukovsky along with NEK was developed and tested a unique method of sulphur cover testing using a full-scale rail car model in wind tunnel (WT) T-101.
Fig.3. Wind tunnel T-101 (http://www.tsagi.ru/), the biggest one in Europe.
With the priority as of October 27, 2011, NEK and the Federal State Unitary Enterprise TsAGI (Central Aerohydrodynamic Institute named after N.E. Zhukovsky) received Eurasian Patent No. 017023 for invention "Stand to test flexible cover of railroad open rail cars, model of an open rail car, test method of flexible cover (options), as well as their application for test flexible cover".
Fig.4.Stand to test sulphur cover in the full-scale rail car model. The open rail car was placed on three vertical stands of aerodynamic balance in the open part of the wind tunnel T-101. The airflow is moving from the left to the right, from the nozzle to the diffuser.
During the tests, the airflow speed of WT varied from 65 to 162 km/h, during the experiments changes also: the height of the cover fixing above the goods surface; direction of airflow; construction and fiberglass of the cover, durability of the cover fixing to rail car walls, durability of diagonal lacing and its type. All covers from different manufacturers were tested at the same conditions. During the test the speed of the airflow constantly increased until the critical value, when the construction of the cover began to crumble. The experiments were recorded on video and photos. Determined also the values of aerodynamic forces acting on the flexible cover and rail car.
Fig.5. Coverage breakoff from the rail car in WT with the wind speed being up to 45 m/s.
The experiments confirmed the negative impact of aerodynamic forces on the cover at increased speeds of airflow, and particularly, if there is crosswind. During a number of experiments on blowing off in the wind tunnel joints of canvas were destroyed, eyelets fastening to the cover were break off from the cover, cover fabric was torn, as well as its extra strong lacing, cover itself detached from the rail car walls, which resulted in its breaking off.
Fig. 6. The cover behavior in WT at flow speed V=18 (a); 28 (b) and 45 (c) m/s. The flow direction is from the left to the right. Severe destruction of cover fabric, tape to fasten the cover to rail car and strapping tapes when the flow speed is increased from 28 to 45 m/s can be seen.
Typical places of cover and auxiliary elements damage were detected; specific zones along the rail car length were identified. Were found low-density zone (air dilution zone) and the ones of airflow compression over and under the cover, by the presence or absence of whirling. There was detected vibrational amplitude of specific points of the cover in the zone of turbulence and loads in the places of cover fixing to the walls of rail car.
According to the results of joint work, with the priority as of August 9, 2012, NEK and Federal Unitary Enterprise TsAGI (Central Aerohydrodynamic Institute named after N.E. Zhukovsky) received a utility model Patent of the Russian Federation No. 124643 “Means for transportation of bulk rail cargo, namely: flexible elastic cover, clamping element for its fixing, railroad open rail car with cover and railroad rolling stock containing at least one such open rail car”. It should also be noted the importance of ensuring the necessary and sufficient tensile strength of tapes. This requirement applies to tapes for fastening the cover to the walls of rail car and to tapes for cross-diagonal lacing cover.
The results of joint work of NEK and TsAGI were published in the «Railway transport magazine» No.7, 2012, and in the magazine «Bulletin of the All-Russian Research Institute of railway transport» No.3, 2012.
Average binding devices of rail car partially torn from the walls of rail car when performing loading and unloading. Therefore, over time, the quality of cover sulfur decreases. The reason of separation binding devices is as follows. First, when loading sulfur on binding devices affects container that have a load of sulfur weighing up to 30 tons. Secondly, when unloading cargo sulfur a binding devices are damaged grapple weighing 5 tons. Grapple damages not only binding devices, but the walls of the car. It was necessary to reinforce the fastening of the binding devices to the walls of the wagon. Moreover, when fixing the cover in the car to ensure no air gap between the cover and the surface of sulphur cargo, bulk density, which is subject to change.
To fix sulphur cargo cover (various bulk density – from 1.1 to 1.4 t/m3) and attaching the binding tape, it was proposed to use pierced metal corner plate with holes on both sides. The number of holes on one side of the corner plate is equal to the number of holes on the other side of the corner plate. Holes are located at the same distance from the corner plate bottom. Corner plates are welded vertically to the inner walls of the open rail car, with the entire length of both corner plate edges touching the walls. Coverage of sulphur cargo is fastened around the perimeter of the rail car by means of tape tailing to the holes of the pierced metal corner and eyelet holes. Cross binding with a strapping tape is carried out in addition.
With a priority date of May 30, 2012 the company NEC was granted RF Patent for useful model number 133475 "Comb of binding devices for fastening rigging device to the inner walls of open rail car; open rail car with binding devices and open rail car."
Conducted joint scientific and practical researches of NEK, TsAGI and TCO made it possible to develop practical recommendations to improve the quality and durability with regard to the cover of sulphur cargo along the route. Although only part of such recommendations has been implemented due to the cash expenditure limitation, cases of ignition of TCO sulphur cargo have decreased a lot.
Work on sulphur coverage improvement in open rail cars is still in progress.