Sulphur storage

 

A sulphur block at Shantz, Alberta, Canada

Sulphur block at Shantz, Alberta, Canada (2003)

 

When prices are low, liquid elemental sulphur is poured into large blocks to solidfy (sulphur freezes at about 115C) on the prairie landscape for long term storage. Later, when prices are higher, it is remelted, prilled, and shipped to market (often to China). This block is near Cremona, Alberta, Canada. There were a couple dozen such blocks in Western Canada, mostly in the Rocky Mountain foothills, close to sour gas production facilities. Many have been recently melted and sold to market. In this 2003 photo, the vertical wall here is about 25ft tall. The blocks are beautiful.

Elemental sulphur is a dangerous material and care is taken in safely storing this material. Dust from the block can get onto your skin and cause irritation, especially around the eyes. If the block catches fire, it makes a deadly cloud and its difficult to extinguish if the fire gets large. Thiobacillus bacteria colonizes the blocks (this is the main bacteria that contributes to acid rock drainage in mines). It helps convert elemental sulphur to very strong sulphuric acid.

I was fortunate to work on sulphur storage with Syncrude and Alberta Sulphur Research Ltd (University of Calgary) from 2002-2004. One long autumn weekend, I toured about a dozen blocks around Alberta, making geotechnical and geochemical observations, talking to operators, and taking a lot of photos. I learned a lot and was able to apply a geotechnical and geological eye to these wonderful landforms.

Many people used to think that sulphur blocks had very low permeability (hydraulic conductivity). That rain and snowmelt water simply ran off. That they were monolithic blocks. The acid that runs off presents a hazard to surface water and groundwater, so many people tucked HDPE plastic liner under the toes of the blocks and directed the water to neutralizing ponds.

They should have talked to the operators, who would have told them the rain water mostly flowed into cracks in the blocks and often sprayed out the edges, carrying the sulphuric acid with it. But where the blocks were placed on gravel foundations, the acidic waters simply flow down to the groundwater table, and out in nearby streams and wetlands. A proper liner, capable of withstanding the acid attack, is crucial to protect the groundwater environment.

The cracks originate partially from the crystallization of the sulphur. As it solidifies from a liquid, it first turns into monoclinic crystals, then later to orthorhombic. There is a small volume change that causes cracking. But more important, there is a volume change as it cools, and polygonal cracking forms — much like columnar basalt — the structures that form when certain natural volcanic lavas cool. In fact, sulphur behaves a lot like runny pahoehoe lava .

The vertical fractures connect with horizontal ones, and results in very high permeabilities — more like gravel than rock. Almost none of the water evaporates, it almost all percolates into the block. The block is about 4 to 7% voids due to the cracking.

 

Here are some pictures from the 2003 tour that highlight some of the items noted above:

Molten sulphur is dark orange. Sulphur has a melting point of 115C.

Molten sulphur is dark orange. Sulphur has a melting point of 115C.

 

Sulphur is poured in thin lifts -- like flooding an ice hockey rink. It solidifies at 115C and has strengths like weak concrete. It is formed into these massive blocks.

Sulphur is poured in thin lifts — like flooding an ice hockey rink. It solidifies at 115C and has strengths like weak concrete. It is formed into these massive blocks.

 

Sulphur cracks due to thermal shrinkage and crystal changes. It forms highlight permeable structure -- water flows right through it. The black is thiobacillus bacteria which catalyze the formation of sulphuric acid.

Sulphur cracks due to thermal shrinkage and crystal changes. It forms highlight permeable structure — water flows right through it. The black is thiobacillus bacteria which catalyze the formation of sulphuric acid.

 

Older blocks tend to spall -- perhaps due to freeze thaw.

Older blocks tend to spall — perhaps due to freeze thaw.

 

 

 

Corners are particularly prone to spalling -- sort of like a brick wall without the overlapping bricks.

Corners are particularly prone to spalling — sort of like a brick wall without the overlapping bricks.

 

 

 

A patented sulphur remelter is used to convert the solid sulphur back into liquid so it can be pipelined, trucked, or converted into prills for rail transport to an ocean port.

A patented sulphur remelter is used to convert the solid sulphur back into liquid so it can be pipelined, trucked, or converted into prills for rail transport to an ocean port.

 

 

Polish prilling machine -- this vertical wind tunnel turns molten sulphur into little prills -- pure sulphur granules about the size of rice crispys. A train takes these to port. Most sulphur is converted into fertilizer.

Polish prilling machine — this vertical wind tunnel turns molten sulphur into little prills — pure sulphur granules about the size of rice crispys. A train takes these to port. Most sulphur is converted into fertilizer.