Perspectives and possibilities
6th Potsdam Technical Conference „Optimisation in the Thermal Treatment of Wastes and Residues“, Potsdam/Germany (19.–20.02.2009)
“One has to demand the impossible in order to achieve the possible” – this quotation from Helmut von Moltke served as the keynote for the 6th Potsdam Technical Conference. This conference, which has meanwhile become a regular event in February, was attended by about 150 experts from not only the actual thermal treatment sector for wastes and residues but also from plant construction and related sectors.
On 18.02.2009 a limited number of participants had already taken part in an organized excursion to the refuse incineration plant at Berlin-Ruhleben. This refuse incineration plant of the city sanitation department, with its annual capacity of more than half a million tonnes, is the key element of the Berlin refuse disposal concept. The incineration plant for municipal solid wastes in Ruhleben – inhouse designation “Refuse Processing Plant North” – has been in operation since 1967. Up to its final completion in 1974, eight boiler lines with a throughput capacity of 400 000 t per year were installed. A flue gas purification system was added in the 1980s, involving an investment cost equivalent to around € 400–500 million at today’s rates. In order to ensure constant compliance with the increasing demands on environmental compatibility, the plant was upgraded to the latest technological standard between 1996 and 1998 at a cost of approx. a quarter of a billion €. Since the 1980s, advances in process technology have reduced the pollutant emissions of modern refuse incineration plants to between one tenth and one hundredth.
After the conference was opened by Lutz-Peter Nethe of Texocon Potsdam, the programme of presentations commenced with “Application of the SCR process for NOx reduction”, by Dr. Wolfgang Schüttenhelm of Argillon GmbH, Redwitz/
Germany. Optimum integration of an SCR system in the overall plant concept results in the following main benefits:
– high NOx removal with lowest fugitive ammonia
– combination with dioxin and furan removal
– applicable in low and high-dust areas
– combination with semi-dry and dry processes enables low-temperature SCR.
Reinhard Pachaly, contractual partner of ERC GmbH provided a detailed survey of the SNCR process in his paper “Optimization and retrofitting of SNCR systems for NOx limit values below 100 mg/Am3”. He reported on experience with systems designed for this limit value and on measures for upgrading existing systems. The possibilities for upgrading existing systems depend on the quality of the firing system and on the employed reducing agent.
The paper “Catalytic NOx removal at low temperatures”, presented by Ruedi Frey of Roll Inova Zürich/Switzerland, showed that even at 180 °C the activity of conventional DeNOx catalytic converters is still high enough to assure adequate flue gas purification. On the basis of examples he demonstrated how the catalytic cleaning of sulphurous ammonium salts takes place and how the exhaust gas compositions change during this process.
Ralf Koralewska of Martin GmbH für Umwelt- und Energietechnik, Munich/Germany, provided details of the VLN process in his presentation “NOx reduction with the very-low NOx process (VLN)”. The principle of this process is based on the fact that thermal NO plays only a minor role in grate firing systems if nitrogenous biomass or wastes are employed as fuel. Actually, the decisive factor is the fuel NOx mechanism. The VLN process makes use of the internal exhaust gas recirculation (VLN gas) in combination with reduced secondary air pressures in order to lower the oxygen excess in the lower combustion chamber and increase the temperature. As a consequence, those reactions are supported that cause the formation of N2 and thus ultimately lead to reduced NOx emissions.
“More stringent NOx limit values for combustion systems – What significance does that have for plant engineering?” was the question dealt with by Christian Fuchs of LAB GmbH, Stuttgart/Germany. In his paper Fuchs discussed the individual parameters such as catalytic converter material, catalyst poisons, different system configurations and pure gas values. To summarize, he stated that the currently available technology is able to meet the demand for average annual figures of less than 100 mg/Am3, both with SCR and with SNCR systems.
“Answers to the increasing demands on flue gas purification systems downstream of combustion systems as regards removing HCl, SOx and NOx on the basis of industrial examples” were provided by Rüdiger Margraf of LÜHR FILTER GmbH & Co. KG, Stadthagen/Germany. When demands on the cleaning increase, for example due to permanently higher chlorine and/or sulphur contents in the fuel or when lower emission limit values are required, for instance 50 % of the 17th Federal Immission Control Ordinance values, the reagent consumption of the processes already discussed rises disproportionately. Margraf proposed that sorption processes should be considered as an alternative in order to achieve such aims. One well-suited process variant for these applications is, in the opinion of the author, the two-stage conditioned dry sorption with counterflow reagent infeeding. LÜHR FILTER already possesses many years of operating experience with this process, including applications in thermal residue disposal systems.
Henk Hofmann of Online Cleaning Germany GmbH, Haan/Germany, introduced the possibility of “Shutdown avoidance by means of explosive cleaning while the plant is in operation”. He particularly stressed the financial savings to be achieved by avoiding stoppage times.
“Electrostatic precipitator refurbishment as exemplified by AEB Amsterdam” was the subject dealt with by Hans Ulrich Heiland and Ralf Kleinwechter, GBT Bücolit GmbH, Marl/Germany. Their presentation covered the procedure for refurbishment, optimization and coating of an electrostatic precipitator used for residue collection in the Amsterdam refuse incineration plant.
“Fire and explosion protection for thermal refuse treatment plants” was presented by Dr. Ralph Semmler of Müller BBM GmbH Düren/Germany. To summarize, Dr. Semmler pointed out that as a result of the sometimes very special requirements imposed on fire and explosion-protection systems it is highly recommendable to obtain the advice of fire and explosion-protection experts at an early stage before applying for a permit to construct or modify a thermal refuse treatment plant.
Rüdiger Madla of MEAB mbH Neu Fahrland/Germany presented the “Technical implementation of a concept for homogenising the waste input in a hazardous waste incineration plant”. Madla observed that requirements primarily go in two directions:
1. Complex systems
In addition to the basic functions of grinding, blending and pumping, the plant has to perform other functions, such as the removal of specific material types. In this connection, resource recovery is placed before thermal treatment.
2. Cost-effective systems
Most of the built hazardous waste incineration plants are operated at a maximum throughput of 5 Mg/h. at a mixture volume of approx. 10 m³. To provide further fuel preparation capabilities in these times of scarce raw material resources and frequently expensive high-temperature incineration, hazardous waste incineration plants built at approved sites could offer service functions for third parties with throughput rates varying both upward and downward.
“Optimized Hg separation from the flue gas of a hazardous waste incineration plant with discontinuous short-term inputs of high contents into the combustion process (Fig. 1)” was the title of the presentation by Dr. Siegfried Artmann and Wolfgang Zieger of HIM GmbH Biebesheim/Germany. Tests were performed over a period of around
12 months at the optimized system of line 1. Quantities of mercury salts weighed in containers and varying up to 2.1 kg Hg/container were input into the combustion process. The temporary separation stages of NETfloc SMF-1™ fed in metered quantities into the FK II and activated carbon fed in metered quantities downstream of the scrubber both went into automatic operation properly after a raw gas value of 30 000 μg/Am3 was exceeded, so that no emission could be measured in the clean gas. In the presence of relevant CO concentrations in the flue gas and a corresponding flue gas moisture content, the HgSO4 already bonded in by chemical sorption can be reduced to Hg0 and cause significant emissions in the clean gas.
“Optimization of the refuse incineration lines of the Asdonkshof waste disposal centre”, presented by Hans-Georg Kellermann of the Kreis Weseler Abfallges. mbH & Co. KG, Kamp Lintfort/Germany, explained the upgrading of the firing performance control system, and the modifications to the grate and boiler systems, the flue gas purification process, the induced draught system, water/vapour systems and the turbines.
Dipl.-Ing. Reiner Kissmann of Wallstein Ingenieurgesellschaft mbH/Germany, then presented “Optimization of thermal waste and residue treatment” which dealt with the conversion of the blowpipe quencher made of graphite in the refuse incineration plant AEZ Asdonkshof (Kreis Weseler Abfallgesellschaft mbH + Co. KG) to a “Venturi quencher”. The conversion brought an increase of about 15 % in refuse throughput, resulting in an increase in fresh vapour capacity from approx. 47 to 55 tph.
The paper “Bio-electrical gas cleaning BEGA – the new development in the field of odour removal; development of the process and initial practical experience” presented by Robert Mnich of Junker Filter GmbH Sinsheim/Germany described a new development that combines the technologies of electrostatic and biological exhaust air cleaning.
Robert A. Mergler of Bamag GmbH Butzbach/Germany titled his paper “Present-day sewage slurry incineration – reliable residue treatment exemplified by St. Petersburg”. It described the construction of a mono-sewage slurry incineration plant with a daily treatment rate of 44 t of dry matter. The pre-dried slurry from the sewage treatment plant is burnt in a modern fluidised bed system. The overheated process vapour produced generates electricity via a turbine.
The presentation by Günther Weiß of Energieversorgung Offenbach AG was concerned with “Increasing the energy efficiency of a refuse incineration plant by modifying the flue gas reheating system”. His conclusions: Apart from the availability and the attainable incineration prices, the energy efficiency is taking on an increasing importance for the overall profitability of refuse incineration plants. Provided that the existing catalytic converters and the local conditions permit, one measure resulting in significant savings is to replace the natural gas burner for flue gas reheating with a heat exchanger supplied with fresh steam.
Dr. Martin Mineur of Vattenfall Europe New Energy GmbH Hamburg/Germany reported on “Operating experience and problems with corrosion in the flue gas routes due to manufacturing defects in the vapour gas preheaters exemplified by Müllverwertung Rugenberger Damm”. Dr. Mineur vividly described the fault localisation efforts when it was no longer possible to heat up the flue gas to the required temperature in the flue gas cleaning system after the vapour gas preheaters had been replaced. As a consequence, considerable corrosion damage was suffered as a result of temperatures below the dewpoint. This included failure of an induced draft duct with subsequent emergency shutdown of a refuse incineration boiler. Finally the cause was found to be the foil coating made of PTFE, which corrugated when hot and thus hindered the heat transfer.
Rolf Waller of Stadtwerke Rosenheim GmbH Co. KG presented “Measures for increasing efficiency and capacity in the Rosenheim waste-to-energy plant” (Fig. 2). According to a technical and economical feasibility study, the alternative additive sodium bicarbonate can only be used economically in conjunction with an additional heat extraction. The measure for increasing the energy efficiency in combination with the use of sodium bicarbonate was recognized in June as one of the 10 best projects within the framework of the Baverian Energy Prize 2008.
“Does a lot help a lot?” asked Martin Sindram of Rheinkalk GmbH/Germany in his paper on the subject of “Efficient reagents in the flue gas purification process for industry and for power stations burning secondary fuels and biomass”. He described the dry and semi-dry flue gas purification processes (Fig. 3) and provided an overview of the development of highly-reactive lime-based adsorbents. On the basis of industrial examples he also reported on already-performed optimisation measures and the achieved increases in capacity at existing plants.
Andreas Wecker of the Bundesverband der Deutschen Kalkindustrie, Cologne/Germany spoke about “Conditioned dry sorption – an ecological challenge!”. Under the preconditions and assumptions of this comparative analysis, alternative scenarios with SNCR systems lead to the conclusion that the use of calcium hydroxide leads to clear ecological advantages. The precondition is an optimized design of the SNCR system, because the benefits of dry sorption must not be gained at the expense of higher NOx emissions (also see ZKG 6/7-2009, P. 30).
In his presentation “Optimized activated carbons for the separation of dioxin and mercury” Jürgen Fritzsche of CarboTech AC GmbH, Essen/Germany comprehensively discussed the working principle and the properties of activated carbon. Impregnation of the activated carbon with different chemical compounds decisively influences its effectiveness for flue gas purification. In the last section of his presentation, Fritzsche also covered silo design and used a concrete example to explain the removal of heavy metals from flue gases.
“MCS100FT – a new multi-component emission measuring system certified acc. to EN15267-3” was presented by Dr. Michael Boness of SICK MAIHAK GmbH Meersburg/Germany. The new multi-component emission system was primarily developed for die measuring the smallest traces of HF, as demanded by European law (EN 2000/76). Furthermore, the system performs continuous and simultaneous measurement of all other relevant exhaust gas components SO2, CO, NH3, HCl, TOC, NO, NO2, CO2, H2O, O2, CH4 and N2O.
Horst C. Gass and Jochen Kolenda of Müller BBM GmbH Berlin/Germany reported on “Quality assurance for measuring devices and our practical experience with the implementation of EN 14181”. They particularly emphasized the importance of involving competent public authorities and vendors of measuring equipment at an early stage during the planning of new plants, because both the designing of measurement points and the measurement itself contain a number of hidden sources of errors.
This extensive conference programme was rounded off with a warm-up, sponsored by Messrs. GBT Bücolit GmbH Marl/Germany, and by an evening event in Kronengut Potsdam, sponsored by Messrs. Wallstein. The 7th Potsdam Technical Conference will be held on 25. and 26.02.2010.
