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Key outcomes:

  • Air quality impact assessment completed
  • Government regulations satisfied
  • Stack height optimisation

What is WtE?

Waste-to-Energy (WtE) facilities have been gaining global interest as a means of reducing landfill usage and mitigating the greenhouse gas impacts of landfill gas. These plants combust waste that has been carefully blended to account for varying calorific values. Several factors, such as waste composition and plant design, affect combustion efficiency. Designs that can accommodate a wide range of calorific values commonly employ moving grate incinerators or gasification plants. The heat energy produced is fed into a boiler to convert water to steam. The high-pressure steam then passes through a turbo-generator, producing electricity.

Although WtE technology benefits the environment by reducing landfill usage and increasing renewable energy generation, the combustion of waste can result in a wide range of emissions that must be understood and dispersed appropriately to ensure safe exposures and air quality for the surrounding community. Carbon monoxide, NOX, dioxins, heavy metals, and particulates are among the typical emissions that can occur.

Contours of pollutant at ground level around a WtE site. Due to dispersion and typical wind directions, the best air quality occurs to the east and west.

Figure 1: Example pollutant ground level concentration of various pollutants emitted from a Waste-to-Energy plant (marked by the red flag). Synergetics used AERMOD modelling for this example.

Air quality assessments

Health and environmental regulators subject the assessment and approvals of WtE facilities to a high level of scrutiny due to the emissions they produce. One of the standard key requirements for EPA approvals is screening-level air dispersion modelling to assess both likely and worst-case emissions. Typically, a plume dispersion model, such as AERMOD, AUSPLUME, CALPUFF or TAPM, is selected in consideration of both regulatory guidelines and conversations with the local regulator. Each of these models has its limitations and results from some of these models strongly depend on its settings. Therefore, a strong knowledge of the sub-models and their workings is required to generate accurate results.
Synergetics’ team has extensive experience in conducting dispersion modelling and assessing the impacts on air quality in the surrounding areas. The assessment models ground level concentration of different pollutants, as per standard guidelines set by regulatory bodies. In addition to approvals, we also conduct optimization studies on stack dimensions. For example, to optimize the stack height and ensure that ground level concentrations are within safe exposure limits for local communities, Synergetics have undertaken air quality assessments for multiple stack heights. In hilly regions, we use topological data with meteorological data to incorporate the effect of variations in the surrounding topology. We also conduct odour assessments for facilities to address regulatory concerns regarding odour emissions from material handling.

For related works, see our Air Quality Modelling summary.