Experiment Title: Efficiency of a Gas Fired Boiler

Applied Energy Engineering

Efficiency of a Gas Fired Boiler

1. SUMMARY

The aims of this experiment were to determine the thermal efficiency of the boiler at steady state for different conditions and to determine the quantity of combustion products; the mass of emissions and moisture at the operating conditions. There are several kinds of boilers. The one used in this experiment is the most commonly used in industry in the UK. Most boil the water to this one which produces hot water similar to a household gas heating system boiler (Zandi, 2010).

After a risk assessment exercise was conducted, Water, Methane gas and air was fed through separate feed pipes to mix and combust in the boiler. There were (variable area) flow meters and control valves; set to 50L/min, 550L/min and 10L/min for CH4 gas, air and water and 75L/min, 900L/min and 10L/min for the second condition respectively. The equivalent temperatures were measured by a set of thermocouples at a 3-minute time interval as changes in temperature were measured for the flue gas (T1), outlet water(T2), pipes of water in the boiler (T3), inlet water(T4), and flame temperatures (T5) for a total time of 45minutes for the two conditions separately. A rig diagram and risk assessment are presented on pages 3 and 4.

The temperatures were recorded with a PT-100 temperature sensor and a K-type thermocouple; the concentrations of CO₂, CO and O₂ in the flue gas were analyzed using a K-940 handheld combustion analyzer and a conditioner coupled to the sampling point, providing real time data. The flow meters were observed for changes, refer pages 5 and 6.

The heat produced by the combustion of the gas, Q, heat take away in the flue gas, QF, heat taken up by the water, QW, heat losses, QL and thermal efficiency were calculated. The energy balance was prepared to determine the quantity of emissions and moisture from the reaction using standard equations (Goodger, (1977) and Turns, (2006). Refer to pages 9 and 10.

In the first condition, the values of QF, QW, QL were as 1551.96KJ, 47,589KJ and 29,248.74KJ respectively while values for the second condition the values of QF, QW, QL were 1826.96KJ, 41,005.8KJ and 74,752MJ respectively.. The thermal efficiency values were 60.71% for the first condition and 34.87% for the second. The equivalence ratio obtained from 476.19L theoretical amount of O₂ was 0.87 for the first condition and 0.79 from 714.29L theoretical amount of O₂ for the second. The quantity of combustion by-products for both conditions as calculated is tabulated and all these are shown from page 10.

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