The Use of Three-Dimensional Numerical Air Pollution Models In Planning Plant Location Design And Operation
Authors: Lantz R.B. , McCulloch R.C. , Agrawal R.K. 
Published: March 2010

The costs associated with plant location, construction, design and operation are, to a considerable extent, influenced by air quality requirements. Standard analytical methods for predicting the environmental impact of plant emissions do not consider:the effect of terrain in modifying the wind field.transient winds orthe cumulative effects of multiple sources, except in an additive manner.

These factors can greatly affect pollutant concentrations and need to be considered in plant planning to avoid future costly modifications and for efficient plant operation.

This paper discusses the use of a comprehensive mathematical model that describes wind flow over or around topographical features, simulates transient wind conditions and simultaneously solves for the pollutant concentrations caused by multiple sources. The applications described in the paper include determination of plant location, plant design and operation in areas of complicated topography, and the determination of monitor locations. Also discussed is the use of the model in conjunction with monitors Lo provide complete areal and vertical coverage of pollutant concentrations.

INTRODUCTION

During Recent Years, environmental impact statements have become one of the primary considerations involved in the utilization of natural resource. Today a company is expected to show that its operations whether for new or existing plants - are not causing emissions which harm the environment on either an instantaneous or cumulative basis. A comprehensive mathematical model which defines the ambient concentrations from given emission levels can help provide these necessary impact statements.

Ambient monitoring and mathematical modelling are a tremendous complementary team. Ambient monitoring cannot provide the impact statement of process changes of a new plant except after the fact. On the other hand, mathematical modelling may not have the desired precision unless controlled by matching measured concentration and/or wind velocity data. This may sound contradictory when considering a new plant - but it is not. One of the first requirements for a good environmental impact statement is the definition of background concentration level before the new plant or an operational change is introduced. Through history-matching measured data, a numerical model which includes all important aspects of the problem can accurately predict either the additional impact due to new plants and increased throughput or the reduced impact due to abatement equipment being installed.

Problem Areas

Perhaps the mathematical models most widely used in providing impact statements are the Gaussian plume models (1,2,3). Unfortunately, these models have a number of restrictions which limit their use particularly limiting are the assumptions of how terrain can influence the wind and the restriction to steady-state, uniform wind velocity.

The two assumptions most often used with the plume models concerning terrain influence on wind are:the wind streamlines remain horizontal and intersect terrain orthe wind always flows parallel to the ground surface.

An application problem contained in the paper evaluates these assumptions as they compare with the three-dimensional numerical model results.

Several recent presentations have described methods which can include topographic effects(4, 5. 6) or large urban buildings(7,8).