CCS Opportunities in NSW

The impetus for Carbon Capture and Storage (CCS) technology is the observed impact of CO₂ on climate change.

Implementing CCS represents a significant additional economic and social cost in terms of:

• additional equipment maintenance and other running costs;

• a significant drop in net fuel efficiency and consequent faster resource consumption;

• a significant increase in transportation infrastructure and its environmental impacts; and

• some very real additional dangers and safety issues. 

The climate gains made need to more than offset these costs.

In 2005-6 World fossil sourced CO₂ production is estimated to have totalled around 28,431.7 million tonnes (from all sources including petroleum)[3].  That year NSW sourced coal released 384.3 million tonnes of CO₂ worldwide[4]. NSW coal therefore contributed about 0.13% of the total CO₂ released. Of this total, around 91 million tonnes of coal sourced CO₂ was released in Australia, predominantly in NSW.

Capture

In 2005-6 around 72% of domestic coal consumption was by electricity generators (65.5 million tonnes); 24% by iron making (21.8 million tonnes); and most of the balance to cement manufacture and smaller furnaces.  Lime calcination, the conversion of limestone (CaCO3) to lime (CaO), for cement, releases significant additional quantities of CO₂ (0.8 tonne per tonne of cement produced plus the energy used to heat the process and transport the materials). 

The main metallurgical consumer of coal in NSW is iron smelting at Port Kembla.  This initially produces coke oven and blast furnace gas that is distributed around the plant and used as a furnace fuel and for cogeneration of electricity.  Dissolved carbon in the iron is subsequently converted to COxin the steelmaking process.  While it is conceivable that the CO₂ eventually released by various processes could be captured, the diversity of release points would make capture and subsequent separation very difficult and costly to implement within the present technological paradigm. 

The Aluminium industry also uses carbon to reduce the oxide but the energy required is provided by electricity (from coal fired stations) and the main source of carbon is from petroleum (as petroleum coke). The scale of CO₂ release is an order of magnitude smaller than iron and steel making but capture may be as feasible if the flue gas was processed with that from a nearby a coal burning power station.  Both NSW based aluminium smelters are in the Hunter Valley, near the power generation.

Cement calcination plants are relatively smaller in scale again, and more geographically disperse. They would need additional equipment and energy to capture and process, then transport, the exhaust CO₂ and the difficulties involved would probably preclude capture. 

The best prospects for CO₂ capture in NSW are the coal fired power stations, predominantly in the Hunter Valley.  In theory the full CCS applied to the CO₂ emissions from coal fired electricity generation could reduce overall fossil fuel based emissions from NSW (including those from petroleum and gas) by as much as 25%.  A CO₂ reduction target on this scale requires that all of the CO₂ from coal powered electricity generation (including that from existing power stations) is successfully captured and stored.

There are substantial technical problems (that translate into increased costs) in converting the existing Hunter Valley stations to capture the CO₂.  These stations are air fired so that most of the input (and output) gas is nitrogen (78% of air).  Nitrogen is semi-inert so most passes through the furnace unchanged but it is heated and leaves the plant at above boiling point so energy is consumed.  Raising the combustion temperature by injecting oxygen increases the small proportion of nitrogen that is oxidised to produce troublesome NO_x pollutants.  In addition to nitrogen, CO₂, NO_x, and water vapour; the oxides of sulphur SO_x, ash particles and some other trace elements, including compounds of mercury, are present in the flue gas. If allowed to fall below boiling point before being released the oxides react with the water vapour to make liquid acids that can do serious damage to equipment. Under CCS the CO₂ component needs to be flushed out of this gas mixture (captured) and compressed. Several separation technologies are being trialled with some success, including ammonia absorption, but the potential costs and unsolved difficulties remain daunting.

The capture stage can be facilitated if the nitrogen is not fed into the furnace in the first place.  This requires a tonnage oxygen plant (common in the steel industry) to feed the combustion. This together with preliminary coal gasification can provide other benefits including improved combustion and thermal efficiency (at the expense of additional energy, capital, maintenance and operating expenses expended in oxygen production) but an entirely different furnace technology is required (to that presently installed) to gain these benefits.

To date trials around retrofitting more advanced Chinese furnace technology have been directed towards less efficient brown coal based plant in Victoria.