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Cogeneration and tri-generation

What is cogeneration and tri-generation?

Cogeneration is the simultaneous generation in one process of thermal energy and electrical and/or mechanical energy¹. 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).

¹ Source: 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

Interim NO_x policy for cogeneration

OEH released the Interim NO_X Policy for Cogeneration in Sydney and the Illawarra which sets out a framework for how we are currently dealing with emissions from cogeneration and tri-generation proposals.

One of the concepts introduced in the interim policy is best available techniques (BAT) emission performance. The interim policy does not define what emission performance is consistent with BAT for cogeneration and tri-generation.

What do we define as BAT?

BAT covers all aspects of a proposal including fuel source, technology selection and controls. The concept of BAT is a key principle in the European Union Directive on Integrated Pollution Prevention and Control.

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.

Source: DIRECTIVE 2008/1/EC OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL of 15 January 2008 concerning integrated pollution prevention and control

What do we define as BAT for natural gas fired reciprocating internal combustion engines?

The NO_x emission standard considered by OEH to be BAT for natural gas fired reciprocating internal combustion engines with a capacity to burn less than 7 mega joules of fuel per second are outlined in Table 1. A financial analysis of NO_x controls on gas fired reciprocating engines was used to develop the BAT emission standards².

² Source: 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: NO_x BAT emission standard for natural gas fired reciprocating internal combustion engines with a capacity to burn less than 7 mega joules of fuel per second

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 NO_x emission standard of 250 mg/m³ applies to all natural gas fired reciprocating internal combustion engines with a capacity to burn less than 7 mega joules of fuel per second in the Sydney and Wollongong Metropolitan Area and Wollondilly Local Government Area. Controlling NO_X 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 consumption².

Outside of the Sydney and Wollongong Metropolitan Area and Wollondilly Local Government Area the NO_x emission standard is 450 mg/m³, as defined in the Protection of the Environment Operations (Clean Air) Regulation 2010. A more stringent NO_x 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 (Air NEPM) goal for ozone.

A NO_x emission standard for natural gas fired reciprocating internal combustion engines with a capacity to burn greater than or equal to 7 mega joules of fuel per second 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 NO_x emissions to less than 250 mg/m³ has been shown to improve as the capacity of the engine increases². 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 mega joules of fuel per second) 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 mega joules of fuel per second).

OEH should be contacted for the specific requirements for natural gas fired reciprocating internal combustion engines with a capacity to burn greater than or equal to 7 mega joules of fuel per second.

² Source: SKM 2009, Department of Environment and Climate Change (NSW) Financial Analysis of NOX Controls on Gas Fired Reciprocating Engines, Sinclair Knight Merz, June 2009

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

OEH has firstly defined BAT for natural gas fired reciprocating internal combustion engines 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.

What's happening with the interim NO_x policy for cogeneration?

OEH is continuing to progress the broad framework introduced in the interim policy. Keep a look out for updates to the OEH website on progress with the interim policy and opportunities to provide comments.