Panagiotis Vourliotis

Coal combustion with simulated gas turbine exhaust gas and catalytic oxidation of the unburnt fuel

Abstract One method of improving the overall efficiency of a power plant or increasing the power output is to re-power the existing boilers, using gas turbines in a combined cycle system. For the case of coal-fired plants, this option known as gas turbine topping is limited by the difficulties in coal burnout due to the low oxygen content (12 vol%) in the exhaust gas of modern gas turbines. A possible option to resolve the problem could be the introduction of an oxidation catalyst in order, first, to avoid the incomplete combustion of the coal and, second, to decrease the CO and CxHy emissions. This paper presents the results of coal combustion tests in an existing atmospheric fluidized bed with simulated gas turbine exhaust flue gas. The purposes of the trials were the examination of the possibility to achieve the combustion of low-grade lignite with about 12–14 vol% O2 content in the turbine exhaust gas and the experimental investigation of the catalytic oxidation on the burnout behaviour as well as the resulting CO, SO2, N2O, CxHy and NOx emissions. Two series of measurements were carried out, with and without catalysts. The influence of the catalysts on the burnout of coal and the combustion temperature is examined and discussed. The main conclusion of this experimental investigation is that it is possible to achieve combustion of the low-grade lignite in combined cycle applications, using turbine exhaust gas as a fluidizing and oxidant medium with the support of the catalysts examined in this study, as is shown by the drastic reduction of CO and CxHy emissions.

Emissions during the Co-combustion of Lignite and Waste Wood in a Fluidised Bed Reactor

Co-combustion tests were performed in a lab-scale fluidised bed reactor, in order to define (a) the optimum percentage for substituting Greek lignite by waste wood, and (b) the operation conditions ensuring complete burnout of the fuel blends. Tests were performed at the experimental facility of the NTUA’s Steam Boilers and Thermal Plants Laboratory (NTUA-LSB). Pre-dried lignite, from Ptolemais reserve, and various waste wood species, i.e. uncontaminated wood, demolition timber and railway sleepers, were used to prepare the fuel blends. In all tests, the emissions in flue gases - CO, SO2, N2O, NOx, NO, NO2 and CXHY — were continuously monitored.

Experience on Combustion and Co-Combustion of Greek Brown Coal in Fluidized Bed Facilities

The paper aims to present the experience gained from the combustion trials of Greek brown coal in different installations, both in semi-industrial and laboratory scale. Specifically, these research activities are separated in two parts, i.e. combustion tests using only brown coal and co-combustion tests with brown coal and biomass. Combustion tests with Greek lignite were realised in three different Circulating Fluidized Bed Combustion (CFBC) facilities. Low rank lignite was burned in a pilot scale facility of approx. 100kW thermal capacity, located in Athens (NTUA) and a semi-industrial scale of 1.2 MW thermal capacity, located at RWE’s power station Niederaussem in Germany. The results include the determination of operating conditions to achieve proper fuel burnout, the examination of the influence of air staging on the temperature distribution inside the reactor and the investigation of the combustion behaviour of the particular fuel type and emitted pollutants. Several conclusions are drawn concerning the necessary modifications and requirements of the plant layout when a large scale CFBC installation is designed to utilize low grade brown coal. Co-combustion tests with Greek xylitic lignite and waste wood were carried out in the 1 MWth CFBC installation of AE&E, in Austria. During the tests, oxygen concentration and CO, SO2 , N2 O and NOX emissions were continuously monitored. Ash samples were collected and analysed for heavy metals content in ICP-AES spectrophotometer. The improved combustion behaviour of this lignite type was more than evident, since it has lower moisture content and increased calorific value. In all co-combustion tests, low emissions of gaseous pollutants were obtained and metal element emissions were lower than the corresponding values anticipated by the guidelines. In addition, lab-scale co-combustion tests of Greek pre-dried lignite with biomass were accomplished in a bubbling fluidised bed. The main purpose of these experiments was to examine ash melting problems and differentiation to the emitted pollutants due to biomass addition. The obtained results of all aforementioned activities showed that fluidised bed is the appropriate combustion technology to efficiently exploit the low quality Greek brown coal either alone or in conjunction with other biomass materials.Copyright

Investigation of the Natural Gas Quality in Greece

Recently the European Commission started a project in order to harmonize the gas quality in the European Union. In 2007, a mandate was published to the European Committee for Standardization for drawing up standards for gas quality parameters for group H-gas. This mandate was in close relation with the Directive 2003/55/EC of the European Parliament. This article presents the results of a survey for the quality of the natural gas, which is distributed in Greece. Random samples were tested for 20 days and the main parameters were recorded and examined. The results indicate a significant fluctuation in the examined gas characteristics.