Abstract

This experimental study follows on from detailed Chemkin-Pro numerical analyses assessing the viability of by-product ammonia (NH3) utilization for power generation in gas turbines (GTs). This study looks specifically at NH3 in the industrial wastewaters of steelworks, resulting from the cleansing of coke oven gas (COG). The by-product NH3 is present in an aqueous blend of 60–70%vol water and is normally destroyed.

An experimental campaign was conducted using a premixed swirl burner in a model GT combustor, previously employed in the successful combustion of NH3/hydrogen blends, with favorable NOx and unburned fuel emissions. This study experimentally investigates the combustion performance of combining anhydrous and aqueous by-product NH3 in an approximate 50:50%vol blend, comparing the performance with that of each ammonia source unblended. Green anhydrous NH3, a rapidly growing research topic, is a carbon-free energy vector for renewable hydrogen. Some potential benefits of combining the two sources are suggested.

Ammonia combustion presents two major challenges, poor reactivity and a potential for excessive NOx emissions. Prior numerical analyses predicted that 15%vol addition of steelworks COG, at an inlet temperature of 550 K, may provide sufficient support for raising the reactivity of the NH3-based fuels, whilst limiting undesirable emissions. Therefore, addition of 10, 15 and 20%vol COG to each NH3-based fuel was investigated experimentally at 25 kW power with inlet temperatures > 500 K, at atmospheric pressure.

As nitric oxide (NO) emissions decrease significantly with increasing fuel-to-air ratio, experiments were conducted at equivalence ratios (Φ) between 1.0 and 1.3, the precise range of Φ for each blend being optimized according to the modeling predictions for emissions. Leading blends, anhydrous NH3 with 15%vol COG and the 50:50%vol blend with 15%vol COG, achieved < 100 ppm and < 200 ppm NO respectively.

Modest-sized steel plants produce ∼10 metric tons of by-product NH3/day. Aspen Plus was used to model a Brayton-Rankine cycle with integrated recuperation. Adopting typical losses (48% cycle efficiency) and ∼1.2 MPa combustor inlet pressure, the net electrical power generation of 15%vol COG blended with 10 tonnes/day of aqueous industrial NH3 and 25 tonnes/day of anhydrous NH3 (i.e. achieving a 50:50%vol blend) was ∼4.7 MW, ∼47% more power than for the same amount of anhydrous NH3 with 15%vol COG. This significant increase, indicates how industrial NH3 could enable green NH3 to power.

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