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Oct-2011

History and origins of sulphur blocking

Although sulphur blocks may not always be the first thing to come to mind when asked to consider the critical components of a hydrocarbon processing operation, they nonetheless play a critical role in both the sulphur supply chain and the operational plan for dealing with sour feedstock.

Eric Harbaugh
Enersul

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Article Summary

Sulphur blocking traditionally consists of pouring sulphur into large, monolithic blocks for storage. In most cases, moveable slipforms or other temporary forms are used to shape the block, although concrete blocks and even dirt berms have been used to form the walls of a sulphur block. It is interesting to ask where and why the idea of building these gargantuan blocks derived, and whether or not this clearly low tech practice will continue to play a role further into the 21st century.

Origins of blocking

It is true that some sort of sulphur blocking has most likely been used in emergency situations for as long as molten sulphur has been handled either as a byproduct from smelting or as a feedstock into sulphuric acid plants. However, blocking first became a common practice in sulphur handling when the Frasch method took hold along the Gulf Coast of the USA. With the drive and entrepreneurial spirit of people like Herman Frasch himself, as well as others like the Brady brothers, a large industry grew from non-existence to dominance of global sulphur production in a relatively short period of time.

Mining, excavation and smelting
However, this type of production possessed distinct differences from the other sulphur sources in existence at the time, namely traditional mining and excavation of shallow sulphur deposits and ore smelting. In traditional mining, the production rate is obviously very simple to control. A mine can easily change the number of workers or adjust the size or number of pieces of equipment in operation in order to adjust the production rate. In addition, the incremental cost per ton is generally flat, so the margin does not change substantially based on the mine’s production rate. Also, the mine can easily shut down and start up with very low cost. Due to this adaptability, a sulphur miner possesses the ability to produce sulphur in accordance with the needs of the customers. There is no need to maintain more inventory than is required to meet customer commitments.

Smelting byproduct sulphur production more closely mirrors the sour oil and gas processing sulphur production that can be seen today. It is purely a byproduct of processing a more valuable commodity, like copper. As a result of being tied to another, predictable process, the production tends to be steady and is known in advance. A smelter knows how much sulphur will be produced well before actual production. Therefore, arrangements can be made for storage, transportation and sale.

The Frasch method
The Frasch method shares none of these characteristics of control and predictability, especially in the early days of the process. Frasch mining generally involves sending a well bore into a subterranean deposit of sulphur. The well usually consists of three concentric pipes. One for injecting superheated water to heat and melt the sulphur; one for injecting compressed air to aid the sulphur flow; and one allows the molten sulphur to flow to the surface for filtering, storage, and ultimately shipment to a customer.

This process requires a large amount of energy to heat and pump the water and air, as well as taking a substantial amount of time for a well to reach a stable production rate upon start up. Once a well begins flowing, the well will typically be produced at as high a rate as possible for as long as possible.

Although experience in the industry has allowed engineers to make reasonable predictions about production rates, this was a fine art, not a mass balance calculation or exercise in stoichiometry. In addition, the flow rates did not necessarily follow a predictable pattern over the life of the well. As a well became more mature, the area of sulphur potentially exposed to hot water might be higher, resulting in higher flow rates, assuming a sufficient volume of hot water was available. However, there were countless other factors that could have the opposite effect.

The bottom line is that Frasch mining had neither the control of traditional sulphur mining nor the predictability of a byproduct of smelting.

Therefore, Frasch producers desperately needed a way to absorb large and fluctuating inventories. Given the obvious costs of molten tanks, they chose to pour the sulphur into forms and build solid blocks. Since sulphur is almost completely insoluble in water and not terribly reactive, it could be stored outside with little or no protection from rain or weather. As a result, these blocks became larger and soon appeared virtually identical to the blocks seen today. A Frasch mine operator would pump the produced sulphur from the ground and onto a block. Usually, the molten sulphur would go through some sort of settling and/or filtration system to remove some of the impurities that would rise up to the surface along with the sulphur. Once it was poured onto the block, it would stay there until needed for shipment to a customer. Although the molten sulphur market grew steadily over time, when Frasch sulphur dominated the market, most international trade was in crushed bulk form. Essentially, the sulphur was simply broken off the block and loaded into rail cars, trucks, barges or ships.

Contemporary blocking
Despite the similarity between the blocks of the early 1900s and today, the methods change just as with any technology. Methods for both building the blocks and recovery of sulphur off the blocks have adapted over time to higher standards of safety and environmental responsibility. The starkest contrasts between the early days of blocking and today lie in recovery of sulphur from the blocks.

Take a moment to consider what a young man from East Texas might do when faced with the following problem: he has one monolithic block of sulphur approximately 40 ft high, 200 ft wide and 500 ft long. He estimates it contains 200 000 t of sulphur that has been pumped out of nearby Frasch mines over the last few weeks. In a week he will need half of that sulphur to be in broken up chunks that he can load into rail cars. When faced with the conundrum of finding the cheapest and fastest way of breaking big, solid things into tiny pieces, the obvious answer is dynamite.
Although other, less spectacular means of demolishing a block were also employed in times past, the fact that dynamite was used extensively illuminates the drastically different safety culture existing in the first half of the 20th century. The days when worker injuries were a known cost of doing business are distant memories of the industrial past. The advancement of worker safety continues to drive most of the industry developments in sulphur blocking and recovery.


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