Wednesday, December 4, 2013

CGS and the Solvay Process

Coal seam gas (CSG) is any naturally occurring gas, such as methane, that is trapped in underground coal seams by water and pressure. Methane, often called natural gas, is a commercially valuable resource, so mining companies drill into the coal seam, pump the water out, which releases the pressure and forces the gases to the surface. Queensland is believed to have about 98% of Australia's coal seam gas reserve. More than 4,000 CSG wells in Queensland account for about 17% of that state's electricity. NSW has about 500 CSG wells.

The water that is produced in coal seam gas mining is not suitable for human consumption. The water is most often very salty and can contain heavy metals and toxic compounds.
A new drilling project in the Pilliga Forest in the north-west of NSW is expected to produce an average of 3 tonnes of salt a day over three years!

That's a lot of salt! Left to itself, lying around near the mine, it will poison land and waterways. So what can you do with all this salt?

Salt, sodium chloride, is an important commercial chemical. It is used to produce chlorine and sodium hydroxide, and is used in other industrial process, it is used directly for snow and ice control, as a mineral in animal diets, as a preservative, as a flavouring agent, and as a reagent for water softening. The total (deliberate) production of sodium chloride world-wide is about 250 million tonnes per year.

One way to get rid of the salt produced in coal seam gas mining is to turn it into something else, sodium carbonate for instance.
In Australia, the Penrice Soda Products company in Osborne, South Australia, operates a plant using the Solvay Process to turn sodium chloride into sodium carbonate.
The overall chemical equation for the Solvay Process is
CaCO3(s)   +   2NaCl (aq)   right arrow   Na2CO3(aq)   +   CaCl2(aq)
 CaCO3(s) is present in limestone and the NaCl is the by-product of the CGS mining.
The company currently produces about 325,000 tonnes of sodium carbonate every year.

Further Reading:

Solvay Process

Suggested Study Questions:
  1. How much NaCl will the Pilliga Forest mining project produce in one year?
  2. Assume that there are 4,500 CSG mines in Australia and they each produce 3 tonnes of salt a day. How much salt will be produced in one year in Australia from CSG mines?
  3. The density of sodium chloride is about 2.2 g/cm3. Calculate the volume of salt produced each day by the Pilliga Forest CSG mine.
  4. Assume a single truck can carry 100 tonnes of salt. How many truck loads of salt will be produced at the Pilliga Forest CSG mine each year?
  5. Give one environmental issue that would be raised in trucking salt over large distances. Explain how the problem could be reduced.
  6. Give one commercial problem associated with trucking salt over large distance using the same truck. Explain how the problem could be reduced.
  7. What is the maximum amount, in tonnes, of sodium carbonate that could be produced using 1 truck load of sodium chloride?
  8. What is the maximum amount, in tonnes, of calcium carbonate required to completely convert 1 tonne of sodium chloride to  sodium carbonate?
  9. If the actual yield of sodium carbonate is 86.2%, what mass of sodium carbonate would be produced from the complete reaction of 1 tonne of sodium chloride?
  10. Assuming the solvay process was used to convert all the salt from all Australia's CSG mines into sodium carbonate, how much sodium carbonate would be be produced?
  11. World production of sodium carbonate is currently about 42 million tonnes per year. If Australia began production of sodium carbonate using all the salt produced in the CSG mines, what percentage increase would there be in world production of sodium carbonate?
  12. What would you suggest Australia do with the salt produced as a by-product of coal seam gas mining?

No comments:

Post a Comment