May 2016

Notes- Paper set by lecturer other than Colin who was on a research sabbatical- content may vary to what has been taught this year.

SECTION 1:

1. A standard coal power station releases several combustion products into the atmosphere via the flue gases (in the absence of any pollution reduction scheme). 

a. Name the five main pollutants of the flue gases. (5 marks)

SOx, NOx, C02, particulate matter (PM), mercury vapour 

b. Describe the methods for cleaning the 5 pollutants from power station flue gases and link each method with the particular pollutant (one sentence each). (5 marks) 

To remove sulphurous oxides from gaseous emissions flue gas desulphurisation can be used which involves the addition of Calcium carbonate to produce Calcium suplate and CO2.

To remove nitrous oxides from gaseous emissions ammonia can be added to waste gases where it will react with NOx to produce nitrogen gas and water.

Post-combustion carbon capture and storage involves washing emission gases with a solvent such as ethanolomines which absorb the C02 and will later release it when heated.

Removal of particulate emissions can be carried out using an electrostatic precipitator which involves passing the gas first through a negatiely charged field where the PM picks up a negative charge and then past positively charged plates which causes the PM to be attracted to the plates and then fall into collector trays.

Mercury vapour can be removed using pulverised actived carbon (PAV) wich when injected adsorbs mercury vapours and can then be collected along with any flash ash. 

2. List three differences in design and/or operation between a standard thermal nuclear reactor and a fast breeder reactor. (3 marks) Explain in detail how to “breed” uranium 233 from thorium 232. (5 marks) Suggest reasons why this process is of special interest in India. (2 marks)

Fast breeder reactors are similar to thermal nuclear reactors except that they do not have moderators in the reactor core to slow down the neutrons. This means fast neutrons are produced instead of thermal neutrons and temperatures can exceed 600oC. Due to the high temperature water cannot be used as the coolant so sodium coolants are used in replacement. Fast breeder reactors require a high quality enriched fuel source in comparison to thermal reactors.

Thorium 232 is bombarded with fast neutrons in the reactor core and Uranium 233 is produced. When a neutron then reacts with the Uranium 233 an unstable nucleus is produced which splits in fissile products and energy. 

Thorium nuclear reactions are of great interest to India because not only is Thorium of greater abundance than Uranium but India also has the largest reserves of Thorium globally with 846,000 tonnes estimated by the World Nuclear association, 2017. As India has a rapidly increasing population and energy demand, nuclear reactions with their high energy density could make substantial contributions to meeting this demand. 

3. List five technical solutions based on passive solar designs and /or systems that could be used by homeowners to reduce energy costs.…