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Energy costs continue to be in sharp focus across industry.

The need to optimise process heating – air, tank and oven – is central to this issue

and, according to one of the major manu- facturers in the field,

warrants a closer look at key factors that impact directly on energy usage and thus costs.

Process gas burner manufacturer Lanemark International believes that, with regard to energy usage, the overall operating efficiency of gas fired, industrial, re-circulating ovens or dryers depends upon several key factors. Apart from ensuring that the burner model selection is correctly sized from the outset to match the process heating demands, consid- eration should also be given to the choice of either direct or indirect fired gas heating systems, which includes the selection of the most efficient temperature burner and burner control systems.

“The issue of direct or indirect firing is particularly important and should be addressed from the word go,” says Lanemark’s General Manager, Adrian Langford. “In the majority of cases, the direct fired option should be selected because 100% of the available heat is delivered into the oven. This decision is significant because the operating efficiency of indirect fired heat exchanger systems is typically up to 20% lower – the impact of which on energy usage is self-evident.”

He also draws attention to the choice of temperature and burner control systems. Installations which utilise simple high/low gas only control – switching between pre-

set high fire and low fire rates – maintain a constant combustion air pressure/flow that is set only for the high fire rate. Significantly, there is no reduction when the burner operates at the low fire rate – with the oven temperature typically varying by up to +/– 5°C about the desired set point.

Modulating (gas only) alternatives, where the gas input is controlled by a motorised gas ball or butterfly

valve, feature a

motor/actuator that responds to either 4-20 mA (or 0-10VDC)

control signal or to a direct three-wire output from the oven process temperature controller. 10 SURFACE WORLD december 2013

This arrangement will offer superior temper- ature control, but also sees the combustion air pressure/flow remain unchanged when the gas flow rate to the burner is increased or decreased.

“Neither of these options optimises energy consumption, which is why a modulating gas and combustion air alternative is often the preferred solution,” continues Adrian Langford. “In this case, both the gas and combustion airflows respond directly to the process oven temperature requirement.” However, he highlights disadvantages with ‘traditional’ methods of gas and air modulation which utilise a linked gas butterfly valve and combustion air damper:

a) The burner combustion air fan runs continuously at maximum speed.

b) The linkage arrangement between the gas and air supplies is inflexible and can be prone to ‘sticking’, and ‘progressive mis-adjustment’ through wear in typical process heating operating environments.

c) The burner does not respond to changes in the oven/dryer process airflows and air pressures.

The latest burner control systems, which benefit from the use of electronic variable speed drives, address these issues head-on. Here, the gas burner receives temperature control signals directly from the oven, causing the burner combustion air fan motor speed to increase or decrease accordingly. The changes in combustion air pressure are then transmitted to the latest generation of gas/air modulating control valves – such as the VAV series produced by Kromschroder – so that the gas flow is increased or reduced proportionally.

“The advantages of this scenario can be significant,” continues Adrian Langford. “For example, the efficiency of the burner combustion air fan is maximised by reducing the motor power requirement as the burner heat input is reduced while, importantly, there are no mech- anical linkages. Moreover, any changes in the oven/dryer air pressure immediately in front of the burner are ‘sensed’ by the modulating gas/air valve which adjusts the required heat input accordingly.”

(CONTINUED ON PAGE 12) follow us on Twitter @surfaceworldmag

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