Ecological aspects concerning the combustion of lignite in Romanian thermopower plants

Abstract

This paper focuses on the analysis of thermopower plants emissions with regard to a new indicator, SONOX (SO from SO₂ and NOX from NO_x), which is symbolized by Σ. Based on this method, analysis is accomplished for several Romanian thermopower plants fuelled by lignite.

Conclusions are drawn concerning the possibilities of reduction of the reaction agents for desulphurisation of the flue gas exhausted by the thermopower plants.

Introduction

Refs. [1], [2] discuss two versions of a new methodology for evaluating the impact of thermopower plants (TPPs) on air quality. The pollutants of concern are carbon dioxide (CO₂), sulphur oxides (expressed as SO₂) and nitrogen oxides (expressed as NO_x and meaning NO₂ equivalent).

In the new method, one starts from the values of the respective emissions content in air having similar toxic effects on the human body. The following expression for “Equivalent Carbon Dioxide” was established:

$$({\mathrm{CO}}_2{)}_{\mathrm{e}}=({\mathrm{CO}}_2)+700({\mathrm{SO}}_2)+1000({\mathrm{NO}}_x)$$

Units for the variables in Eq. (1) are kg/kgf if they refer to a kilogram of fuel or kg/N m³ if they refer to a normal cubic meter of flue gas exhausted.

(CO₂)_e represents the concentration of carbon dioxide in flue gases that would have the same negative impact as the accumulated real concentration of CO₂, SO₂ and NO_x for a given situation. CO₂ represents the principal (from the quantitative point of view), inevitable component of flue gases exhausted from the combustion of fossil fuels (coal or hydrocarbons).

In accordance with the Kyoto agreement, CO₂ must be continuously decreased in order to reach the forecast percentile reduction and globally control the greenhouse effect. For the SO₂ and NO_x concentrations in the flue gases, national and international maximum emissions limits have been established. These limits are designed to protect the environment and to minimize TPPs induced pollution [5], [6], [7].

Thus, in European Community legislation, the limits are indicated by specific standards [1]. If Romania wishes to join the European Community by 2007, its TPPs must conform to EU standards.

In reference to Eq. (1), the two pollutants that are restricted, SO₂ and NO_x, might be expressed as one single factor,

$$({\mathrm{CO}}_2{)}_e=({\mathrm{CO}}_2)+\Sigma \text{,}$$

where

$$\Sigma =700({\mathrm{SO}}_2)+1000({\mathrm{NO}}_x).$$

Σ symbolizes the SONOX indicator (SO from SO₂ and NOX from NO_x).

In this discussion, we will analyze the situation of Romanian TPPs fuelled by lignite. We will apply the SONOX indicator, through which high SO₂ emission is offset by reduced NO_x emission. The authors will evaluate several particular cases. Details are given in Refs. [1], [2], [3].

In Romania, at the proposition of compensation theory authors, the competent authority (Department of Industry and Trade) analyzes the possibility to apply this theory, at list temporarily.

The legalisation of compensation theory, even temporary, could have important advantages especially for Romania and other former communist countries, which have not yet gained necessary financial funds for modernization of all TPPs from the environmental protection point of view.