Boilers are units that use the heat from combustion to heat a fluid that transports the energy to the various points where it is necessary. Obviously, in all industrial processes where heat is consumed it is necessary to optimize energy investment by installing equipment in which the losses are the lowest possible.
In most cases, since the combustion gas outlet temperature is at least 230°C, it is possible to recover the sensible heat from these gases, even up to 170°C (in the case of fuel oil), by installing an economizer at the end of the passage of the gases through the boiler, which heats the feedwater thereof.
In general, it can be said that a drop of 10°C in gases allows a fuel saving of 0.45%, representing 0.32 kg of fuel oil per tonne of steam produced. Such fuel savings mean that the installation of economizers from 10t/h is profitable with amortization in less than three years.
Additionally, it is possible to improve boiler performance by adjusting the combustion to optimum levels of excess air, thereby reducing the oxygen content of the combustion gases.
A reduction of 2 points in oxygen content allows a saving of 0.5% in fuel consumption. Keeping this reduced oxygen level in the entire field of regulation of the combustion equipment requires installing an oxygen content measuring probe in the flue, which acts continuously in the air/fuel ratio reaching the burner. This system starts to become profitable as from 10 MW of heat produced.
Another source of heat loss is that produced by a programme of uncontrolled purges, both surface and deep, so it is necessary to study the profitability of equipping the boiler with automated purges with salinity control and automated sludge purges and the possible recovery of heat from these purges by heat exchange with feedwater.
In addition to the performance improvements that may be made in the boilers, a very significant possibility of energy savings is condensate recovery with direct feed to the boiler, thus avoiding “flash” steam leaks in the water feed tanks, so that for every 1,000 kg of condensate fed directly to the boiler, about 8 kg of fuel oil is saved.
In all cases, the Technical Department of SOGECAL S.L. studies the specific problem of each customer in order to provide the best practical solution.