Fire control

A gas burner that produces less nitrogen emissions by between 10 and a 100 times over conventional systems will make it easier and more economical for industry to meet clean air requirements.

Ultraclean low-swirl combustion (UCLSC) technology developed by Berkeley Lab combustion researcher Robert Cheng in California, can be adapted for use both in industrial and residential burners, and could also help to reduce emissions from domestic boilers.

When conventional burners use natural gas they produce nitrogen oxides (NOx), a family of gases that generate photochemical smog and haze which can damage human health. As a result, governments have been introducing regulations forcing NOx producers to install expensive catalytic emission reduction units or gas recycling burners to control NOx release.

The UCLSC burner mixes air with the gas before it burns to ensure the mixture is lean and burns completely.

Natural gas-fired industrial equipment emits around 100 parts per million of NOx, while a UCLSC burner produces below 10.

Cheng estimates that if residential and commercial burners all used UCLSC technology, just under 750,000 tons of NOx per year could be removed from the US atmosphere alone.

UCLSC burners are not only cleaner than conventional ones but can also be produced for the same price. ‘The system is mostly beneficial to commercial and industrial applications for heating and electricity generation of 30kW to over 50MW,’ said Cheng. ‘But it is also appropriate for home heating furnaces and water heaters.’

The system mixes air and fuel in a ratio that produces a lean mixture that burns completely.

Small air jets swirl the premixed flow inside the burner tube which is fitted with a swirler consisting of angled guide vanes around its outside edge. This mixes air with the gas and produces a divergent flow above the burner exit.

The result is a detached flame above the burner, making the system more efficient as the flame does not lose energy to its components as in established systems.Dr. Cheng made the flame stable by replacing a normal burner’s central bluff body with an open channel through the centre.

‘In a divergent flow, the flow velocity decreases away from the burner exit in a linear manner,’ said Cheng. ‘This allows the flame to propagate upstream against this velocity and it settles at the position where the local velocity is equal to the flame speed,’ he said. ‘This is the mechanism that stabilises the detached flame.’

Cheng is now seeking industrial partners to help commercialise the technology.

The cost of UCLSC home systems may be slightly higher than conventional ones as the burner requires the use of a small electric fan to supply the combustion air to the swirler, but the environmental benefits should ensure it is attractive to consumers.