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Environment Protection Authority

Environmental Issues

Air - NSW overview

Reducing cogeneration and tri-generation emissions

Interim Nitrogen Oxide Policy for Cogeneration in Sydney and the Illawarra

Gas-fired cogeneration can be one of the most greenhouse-friendly forms of electricity generation using fossil fuels. However, cogeneration has the potential to adversely affect local and regional air quality as it can emit significant amounts of oxides of nitrogen (NOx).

The Interim Nitrogen Oxide Policy for Cogeneration in Sydney and the Illawarra (20110442CogenNOx.pdf, 3.1MB) sets out a framework for how the EPA is currently dealing with emissions from cogeneration and tri-generation proposals.

What is cogeneration and tri-generation?

Cogeneration is the simultaneous generation in one process of thermal energy and electrical and/or mechanical energy. (Directive 2004/8/EC of the European Parliament and of the Council of 11 February 2004 on the promotion of cogeneration based on a useful heat demand in the internal energy market and amending Directive 92/42/EEC).

Cogeneration is also referred to as combined heat and power (CHP) and makes productive use of the heat that is normally rejected as waste in conventional generators.

Trigeneration is the simultaneous production of electrical and/or mechanical energy, heat and cooling from a single heat source. It can also be referred to as combined heat, cooling and power (CHCP).

What is BAT emission performance?

One of the concepts introduced in the interim policy is best available techniques (BAT) emission performance (Directive 2008/1/EC of the European Parliament and of the Council of 15 January 2008 concerning integrated pollution prevention and control).

BAT covers all aspects of a proposal including fuel source, technology selection and controls.

Best available techniques shall mean the most effective and advanced stage in the development of activities and their methods of operation which indicate the practical suitability of particular techniques for providing in principle the basis for emission limit values designed to prevent and, where that is not practicable, generally to reduce emissions and the impact on the environment as a whole:

Best shall mean most effective in achieving a high general level of protection of the environment as a whole.

Available techniques shall mean those developed on a scale which allows implementation in the relevant industrial sector, under economically and technically viable conditions, taking into consideration the costs and advantages, whether or not the techniques are used or produced inside the Member State in question, as long as they are reasonably accessible to the operator.

Techniques shall include both the technology used and the way in which the installation is designed, built, maintained, operated and decommissioned.

What is BAT for natural gas fired reciprocating internal combustion engines?

The NOx emission standard EPA considers as BAT for natural gas (NG) fired reciprocating internal combustion engines (ICE) with a capacity to burn less than 7 mega joules per second (MJ/s) of fuel is outlined in Table 1. A financial analysis of NOx controls on gas fired reciprocating engines was used to develop the BAT emission standard (SKM 2009, Department of Environment and Climate Change (NSW) Financial Analysis of NOX Controls on Gas Fired Reciprocating Engines, Sinclair Knight Merz, June 2009).

Table 1: NOx BAT emission standard for NG fired reciprocating ICE with a capacity to burn <7MJ/s of fuel

Activity or plant Air impurity Region Emission standard
mg/m3 *

Any natural gas fired stationary reciprocating internal combustion engine

Nitrogen dioxide (NO2) or nitric oxide (NO) or both, as NO2 equivalent

Sydney and Wollongong Metropolitan Area# and Wollondilly Local Government Area

250

* Reference conditions: Dry, 273 K, 101.3kPa, 5% O2
# Defined in the Protection of the Environment Operations (Clean Air) Regulation 2010

Discussion of BAT emission standards

A NOx emission standard of 250 mg/m3 applies to all NG fired reciprocating ICE with a capacity to burn less than 7 MJ/s of fuel in the Sydney and Wollongong Metropolitan Area and Wollondilly Local Government Area. Controlling NOX emissions to 250 mg/m3 has been found to have a minor impact on project financial performance and is unlikely to impact on project viability. The marginal reduction in financial performance is due to the slightly higher fuel consumption (SKM 2009, Department of Environment and Climate Change (NSW) Financial Analysis of NOX Controls on Gas Fired Reciprocating Engines, Sinclair Knight Merz, June 2009).

Outside of the Sydney and Wollongong Metropolitan Area and Wollondilly Local Government Area, the NOx emission standard is 450 mg/m3, as defined in the Protection of the Environment Operations (Clean Air) Regulation 2010 applies. A more stringent NOx emission standard is only needed in the Sydney and Wollongong Metropolitan Area and Wollondilly Local Government Area as air quality in these regions currently exceeds the National Environment Protection Measure for Ambient Air Quality (Ambient Air Quality NEPM) goal for ozone.

A NOx emission standard for NG fired reciprocating ICE with a capacity to burn greater than or equal to 7 MJ/s of fuel has not been proposed. This will be determined on a case by case basis.

In cogeneration and tri-generation applications, the financial viability of post combustion controls to reduce NOx emissions to less than 250 mg/m3 has been shown to improve as the capacity of the engine increases (SKM 2009, Department of Environment and Climate Change (NSW) Financial Analysis of NOX Controls on Gas Fired Reciprocating Engines, Sinclair Knight Merz, June 2009). In cogeneration applications, post combustion controls are likely to be financially viable at approximately 1,000 kW of electrical output (or a capacity to burn approximately 3 MJ/s of fuel) whereas in tri-generation applications the financially viable minimum size for post combustion controls is likely to be in excess of 10,000 kW of electrical output (or a capacity to burn greater than approximately 30 MJ/s of fuel).

The EPA should be contacted for the specific requirements for NG fired reciprocating ICE engines with a capacity to burn greater than or equal to 7 MJ/s of fuel.

Why has BAT only been defined for natural gas fired reciprocating internal combustion engines?

The EPA has defined BAT for NG fired reciprocating ICE due to the significant interest in its installation in cogeneration and tri-generation applications. BAT will be developed for other technologies and industries on a case by case basis.

Do local air quality impacts still need to be considered?

Yes, local air quality impacts still need to be considered even if emissions performance is consistent with BAT.

Emission standards do not take into account site-specific features such as meteorology, background air quality, and other influences such as terrain and building downwash and therefore do not necessarily protect against adverse air quality impacts in the surrounding area. Depending on the sensitivity of the local receiving environment, an item of plant may need to meet emission standards tighter than BAT.

The impact of emissions from activities and plant is determined through an air quality impact assessment which is to be conducted in accordance with the Approved Methods for the Modelling and Assessment of Air Pollutants in NSW.

Page last updated: 18 June 2013