Emissions–related energy indicators

Securing future energy provision based on resource-efficient and environmentally-friendly methods of energy production and energy conversion is increasingly gaining in significance. This has led to a change in attitude towards waste treatment, whereby waste material is much more regarded as fuel for energy consumption rather than simply as refuse requiring disposal. Energy provision has therefore taken on equal, if not more importance than waste treatment, particularly at industrial sites employing waste material as fuel. As a result, the once more common primary fossil fuels such as
natural gas, heating oil or coal have been increasingly substituted by waste material or waste fractions (‘alternative fuels‘).

Since waste material is extremely inhomogeneous in composition and is subject to correspondingly high fluctuation margins, both temporally and in terms of single fractions, flue gas composition from waste incineration is equally subject to fluctuation.

Alongside other political concerns, this predicament was certainly a contributory factor in the legislature‘s decision to raise emission limit values from waste incineration plants as compared with conventional fossil fuel-fired combustion plants, at once both increasing the scope of substances subject to monitoring and placing more stringent limits on emission levels.

This has given rise to extensive developments in the regulation of emission limit values over the last 30 years, from the initial TA-Luft 1974 (Technical Instructions on Air Quality Control) and subsequent TA-Luft 1986, to the adoption of a separate
Bundesimmissionsschutzverordnung (BImSchV - German Federal Immission Control Ordinance) on waste incineration covered by the 17. BImSchV (17th Federal Immission Control Ordinance) of 23 November 1990 (BGBl. [Bundesgesetzblatt - Federal Law Gazette] I p. 2545, p. 2832) [1]. With the adoption of articles 1 and 2 of the Ordinance of 27 January 2009 (BGBl. I p.129) [2] on the safeguarding of quality requirements set out in the 13th and 17th Federal Immission Control Ordinances, the standards applicable to large combustion plants and gas turbine plants set out in the 13. BImSchV and
to waste incineration and co-incineration facilities set out in the 17. BImSchV were amended by means of long-term averages for the mass concentrations of nitrogen oxide emissions, thus establishing the current tightened limits.

These ongoing emission value reductions have led to the majority of existing waste incineration plants having to constantly adapt or extend their flue gas treatment plants. This has led to the many multi-stage and extremely complex plant facilities still in existence today. A further motive for multi-stage plants was the demand present during the 1990s for the extraction of recyclable materials from residue accrued via flue gas purification, such as the production of gypsum via the flue gas desulphurization process within the power plant sector.

Economic considerations have undoubtedly played a major role in improvements in simultaneous systems, such as dry and conditioned dry sorption methods, meaning that emission limit values fall well below those specified in the 17. BImSchV, even
where cost and energy savings are paramount.

Despite the current very low emission limit values, political acceptance of waste incineration is repeatedly called into question and it will ultimately only remain a tolerable option for the future if further reductions in emission limit values are attained.

Proponents and operators of waste incineration plants counter with the argument that the reduction of any one pollutant by even a few milligrams would incur a disproportionate level of additional expenditure on equipment and energy.

The aim of this study is to demonstrate such discrepancies or dependencies between attainable emission reductions and the emissions-generating energy input necessarily incurred by flue gas treatment technologies in attaining those reductions.

The study initially focuses on current investigations and assessments related to this issue, as well as on the legal emission requirements. Due to the wide range of components involved in flue gas treatment systems and their consequent numerous combination possibilities, six different system Variants are presented and compared. It is notable in the context of the present study that both single and two-stage or multi-stage systems are considered in the set of Variants, which differ not only in their structure and additive use but also in their separation capacity. These six basic Variants reflect the systems frequently employed in practice and represent non-congruent procedural steps with their respective target emission levels. Based on the fact that each of these Variants is already in operation in thermal waste incineration plants, the assessment draws on many years of existing operative experience. In order to allow a comparison of the systems and especially of the requisite energy demands for achieving different separation rates and emission levels, the relevant cumulative energy demand (CED)
is ascertained. This means that the energy demand, which itself leads to the release of emissions, is ascertained for the entire life cycle of the plant, from construction, through operation and ultimate plant disposal after a certain period of operation (approx. 20-30 years). Thus, the production of semi-finished products such as steel, aluminium, plastics, etc. and the production of consumables such as lime, sodium hydroxide and ammonia, as well as the electrical energy used in operating the plant are taken into account. An energy demand credit due to high recycling rates and consequent return
to the economic cycle is to be expected for the plant disposal process.

The individual energy demands for the Variants described are determined on the basis of mass, material and energy balances.

In line with experience, the operational phase represents the most energy-intensive phase when compared with those of production and disposal. Since the most significant dependencies between separation efficiency or emission level and the directly opposed energy demand are on the operational and process control levels, the calculation approaches employed draw on practical experience and form part of the inventory analysis.

Evaluation criteria for energy demand at the different emission reduction ratios are educed from the formulation of emissions-related energy indicators. This establishes a set of tools with which to assess emissions-generating energy demand in the context of emission reduction ratios.