Task REINLUFT Umwelttechnik Results of the biofilter pilot test - DAIMLER

Transcription

1 Odour and hazardous emissions abatement of foundries LIFE10 ENV/FI/059 Task REINLUFT Umwelttechnik Results of the biofilter pilot test - DAIMLER Authors: Dr. Franjo Sabo, Stefan Prechel, Jan-Filip Lutz & Thorsten Schneider (REINLUFT Umwelttechnik GmbH)

2 Table of contents 1 Common details Location of biofilter tests Description of technical installation Execution of measurements Duration of biofilter tests Existing biofilter plants at DAIMLER AG Biofilter plant iron casting Measurement results of the biofilter plant in Biofilter plant aluminium casting Measurement results of the biofilter plant in Biofilter pilot plant - Steel casting Description Filter material Pictures of the trial filter Measurements and analytics Common air parameters Measurement of volatile organic carbons (VOC) Filter material analytics Nutrients and DOC (filter material eluate) Humidity Microbiological characteristics Flow characteristics Results Common air parameters VOC measurements with FID Odorimetry Summary

3 1 Common details 1.1 Location of biofilter tests DAIMLER AG Emil-Kesslker-Straße Esslingen am Neckar 1.2 Description of technical installation Steel foundry. Waste gas from the pouring and cooling line. 1.3 Execution of measurements REINLUFT Umwelttechnik Ing. GmbH Immenhofer Straße Stuttgart, Germany. 1.4 Duration of biofilter tests Start of tests: End of tests:

4 2 Existing biofilter plants at DAIMLER AG The Mercedes-Benz plant in Untertürkheim is one of Daimler AG s oldest plants whose tradition and history date back over a hundred years. Untertürkheim is the place where the Mercedes-Benz brand took root, and where the myth of the automobile was created and automobile history written. Today, with around 18,000 employees in seven divisions, Daimler AG s parent plant develops and produces engines, axles and transmissions for Mercedes-Benz passenger cars throughout the world. In addition to the production of engines, axles and transmissions, the Untertürkheim plant is also home to pre-commissioning, handled by the foundry and forging mill, which have partly been there since the origins of the site. Traditionally in the foundry sector the main distinction made is between ferrous and nonferrous foundries. This is mainly because the applied processes in both sectors differ. Nonferrous foundries often apply die-casting techniques. These allow a better surface finish, which is important for many of the aluminium applications. Due to the high cooling rate, castings with a high mechanical strength are produced. However, this technique does not allow the production of massive or large pieces, which require sand casting techniques. The annual production of light metal casting in Untertürkheim is t. 4

5 Ferrous foundries generally apply the lost mould techniques. Due to their greater stiffness and strength, ferrous alloys are used in different applications to non-ferrous alloys. The size of the products that can be produced is almost unlimited. Ferrous metals have a higher melting point and therefore require different melting techniques. Our pilot plant was set up at a DAIMLER foundry producing cast steel. More than t of iron casting are produced here. The plant is situated at the river Neckar underneath a very expensive housing area. Emissions to air are the key environmental concern. The foundry process generates (metalladen) mineral dusts, acidifying compounds, products of incomplete combustion and volatile organic carbons. Noxious emissions from the melting and treatment of metals are generally related to the use of additives and fuels or to impurities in the feed. The use of cokes as fuels or the heating of crucibles with gas or oil-fired burners can cause emissions of combustion products. Also the application of additives in metal treatment processes generates reaction products. The presence of impurities (e.g. oil, paint) in scrap used for re-melting can potentially cause the production of the products of incomplete combustion or recombination and dust. Also any dust generated may contain metal and metal oxides. The evaporation of elements with a high vapour pressure occurs during melting and small particles of metal escape from the bath. Metallic particles are also generated during grinding and finishing operations. In the making of moulds and cores, various additives are used to bind the sand. In the binding of the sand and pouring of the metal, reaction and decomposition products are generated. These include both inorganic and or- 5

6 ganic products. The generation of decomposition products further continues during the casting cooling and de-moulding operations. Dust is a major issue, since it is generated in all process steps, in varying types and compositions. Dust is emitted from metal melting, sand moulding, casting and finishing. Any dust generated may contain metal and metal oxides 2.1 Biofilter plant iron casting In the early 1990s, Mercedes-Benz experienced repeated odour complaints from populations neighbouring its foundries. Evaluation of air pollution control technologies showed that both adsorption and thermal oxidation would bee too expensive. A series of biofilter pilot and technical scale tests (500 to 2000 m³/h) were performed resulting 1993 in the design and construction of a first stage of a biofilter plant at the iron casting foundry to treat an air mass of 6

7 80,000 m³/h. In 1995 the treated air mass was doubled to 160,000 m³/h by adding a second stage Measurement results of the biofilter plant in 2013 The typical removal performance was > 70% of odour at all times at inlet concentrations of up to 1,500 OU/m³ and around 60% of organics at inlet concentrations of < 200 mg/m³. Total air mass: 160,000 m³/h TOC-Elimination: 60 % crude gas before biofilter: 128 mg/m³ cleaned gas after biofilter: 53 mg/m³ Odour-Elimination: 72 % crude gas before biofilter: 657 OU/m³ cleaned gas after biofilter: 180 OU/m³ 2.2 Biofilter plant aluminium casting Because of the very good results in odour elimination of the first biofilter plant at the iron foundry, two more biofilters systems were installed at the aluminium foundry in The picture at the next page shows the two plants. The first stage treating 100,000 m³/h in the background, the second stage built 2006 treating 120,000 m³/h in the foreground Measurement results of the biofilter plant in 2013 The typical removal performance was > 90% of odour at all times at inlet concentrations of OU/m³ and up to 80% of organics at inlet concentrations of < 100 mg/m³. Total air mass: 220,000 m³/h TOC-Elimination: 78 % crude gas before biofilter: 89 mg/m³ cleaned gas after biofilter: 19 mg/m³ Odour-Elimination: 95 % crude gas before biofilter: 4073 OU/m³ cleaned gas after biofilter: 182 OU/m³ 7

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9 3 Biofilter pilot plant - Steel casting Steel is a material of which the (mass) content of iron is bigger than that of any other element, with a carbon content generally lower than 2%, and which also usually contains other elements. At the DAIMLER site, cast steel is melted in electric arc furnaces and then poured into moulds. The air to be treated by the biofilter was sucked off from the casting shop: It derived from the casting of the molten metal into the mould, cooling for solidification and removing the casting from the mould. 3.1 Description The pilot plant is the same as used in the Stahlwerke Bochum trial and integrates a two-stage high-performance biofilter. The container itself has a size of 20 feet and consists of a filter area and the control room. The parameter of residence time is a function of the filter volume and the contaminated air flow rate into the filter. An increase in residence time yields improved biofilter performance. As the size of a biofilter increases, so does its gas residence time and together they increase the price of the biofiltration system. As the contaminated air flow rate is a fixed entity at many facilities due to production processes or designs, a careful balance must be reached between these phenomena in order to maximize the efficiency of the biofilter while simultaneously offering the most cost-effective solution. 9

10 Design of a biofilter must incorporate a variety of crucial parameters in order to produce an efficient and effective system for air pollution control. Once the primary pollutant for remediation has been identified and is known to meet the criteria suitable for biodegradation, controlling factors in the biofilter design such as microorganisms, filter media, filter bed size, filter media water content, filter media ph, influent air contaminant loading, influent air flow, waste-gas temperature, and particulate control can begin to be considered. Filter media is the driving factor behind a successful biofilter and most of the above-listed parameters directly influence the behavior of the media. 3.2 Filter material Abundant nutrient content and large microbial populations make compost an attractive filter medium, which was also used in this trial. Bacteria, fungi, algae, protozoa and viral organisms are all present in compost. The presence of these microorganisms precludes the need for their inoculation into the filter bed, greatly reducing biofilter start-up time or acclimation period. Water retention and consistently neutral ph levels are favorable in compost media. Wood chips were used in conjunction with the compost as a filler to increase porosity and air flow and decrease the likelihood of medium compaction. 10

11 4 Pictures of the trial filter 11

12 5 Measurements and analytics 5.1 Common air parameters The volumetric flow rate and state parameters of the waste gas stream should be determined in analogy with guideline VDI 2066 Part 1 and VDI For this purpose, representative crude gas and clean gas samples are to be taken for each operating condition. 5.2 Measurement of volatile organic carbons (VOC) The detection of organic compounds is most effectively done with flame ionization. Biochemical compounds such as proteins, nucleotides, and pharmaceuticals can be studied with flame ionization as well as other detectors, like thermal conductivity, thermionic, or electrolytic conductivity due to the presence of nitrogen, phosphorus, or sulfur atoms or because of the universality of the thermal conductivity detector. However, typically the biochemical compounds have a greater amount of carbon present than other elements. This means that a particular compound may be more easily detected using flame ionization over the other methods because of higher carbon concentration and also flame ionization's sensitivity. 12

13 5.3 Filter material analytics Nutrients and DOC (filter material eluate) The filter media may also serves as a source of nutrients and nutrient salts for the microorganisms. In odour abatement applications, the ability of the filter media to act as a nutrient and nutrient salt source plays only a minor role. However, in applications involving waste gases poor in nutrients, intermittent operating conditions and waste gases with high organics loads, the micro-organisms rely on additional nutrient supply. This can be partly accomplished via the nutrient salts present in the filter media. However, in some cases subsequent fertilization of the filter media may be needed. The ability of the organic filter media to serve as the nutrient source for the micro-organisms is of particular importance during prolonged shutdowns. 5.4 Humidity Another important function of the filter media is to provide the micro-organisms with sufficient moisture. Otherwise the micro-organisms would have to be continuously sprayed with water. The filter media has an optimum moisture level at the time it is being placed in the biofilter. In order to preclude rapid bed dry-out, the waste gas to be treated must be humidified to the maximum feasible level before being admitted to the biofilter. After pre-conditioning in a humidifier, the waste gas is normally about 95 % water-saturated. This means that it will take up the remaining 5% as it passes through the filter bed causing the latter to dry out. Filter bed dry-out can be counteracted by providing for additional irrigation of the filter media. A particular problem encountered with organic filter media is that it develops increasing hydrophobic effects as the moisture content decreases. This means that material that has become overly dry is no longer amenable to humidification. In most cases, it has to be removed. Overly wet filter media, on the other hand, will lead to water-logging. Under these conditions, the pores of the filter media are filled with water and thus blocked for the gas flow. This not only affects the removal efficiency but also leads to oxygen depletion and hence, insufficient oxygen supply for the microorganisms. While part of the microbial population can adapt its metabolism to anaerobic conditions, this results in metabolic end products which are similar to those formed by decaying organic materials and have a very unpleasant smell. This effect can be reversed by drying the filter media. The method compares the moisture content of the filter media with that of the fresh material and provides information on the amount of water present in the filter media. For this purpose, the filter media is dried to constant weight at 105 C, after which the moisture content can be calculated from the difference in mass. 13

14 5.4.1 Microbiological characteristics Biochemical measures mainly relate to the addition of supplemental nutrients to the filter media and buffering undesirable changes in ph. The objectives of both measures are identical. They must reach the filter media surface, influence it and have a long-term effect in order to minimize treatment intervals. For this reason, granular additives that have a depot effect are preferred for both measures. Dissolved nutrient salts are added via a separate nutrient delivery system. For ph adjustment, water-soluble granular or powdered lime is added to the filter media. These additives should be introduced in particular into those biofilter zones that are first contacted with the crude gas. In co-current biofilter systems, i.e. crude gas and moisture feed at the top, these additives may also be dosed in liquid form. In determining the necessary dosage rates, the following aspects have to be considered: the nutrient demand of the micro-organisms based on their average composition C:N:P = 100:5:1 the proportion of organic carbon in the filter media mixture the average crude gas concentration and/or pollutant load and the removal efficiency to be achieved the fact that up to 50 % of the organic carbon is incorporated into the biomass of the microorganisms losses through wash-out The count of viable bacterial cells provides important initial information about the micro-flora on the filter media. While this method yields quantitative and qualitative data, it does not provide any information about microbial activity. A high bacterial density does not necessarily imply high elimination efficiency. Reference bacterial counts indicative of normal growth are available for the specific media. If the bacterial count determined is significantly below the associated reference count, the conditions for normal biomass growth are not given. The method uses several dilutions of a filter media eluate sample which are pour-plated onto suitable solid culture media. The number of viable bacterial cells on the filter media is subsequently determined by counting the number of colonies appearing on the culture plates. Additional quantitative determinations can be made with the aid of special agars to obtain further information on the micro-flora. 5.5 Flow characteristics For the filter media to accomplish its manifold functions, it must exhibit specific material properties. It may well be possible, that the specific requirements rule out one another, as described in greater detail below. In such cases, an optimum trade-off tailored to the specific application will have to be made in media selection: A uniform structure favors uniform flow distribution and hence, uniform contacting conditions. This, in turn, improves the degradation 14

15 efficiency of the biofilter and minimizes the pressure drop. A sufficient pore volume reduces the pressure drop across the bed of media and hence, the energy consumption. In addition, it improves the drainage effect of the media and prevents water logging. Depending on the type and condition of the filter media, the void volume may range between 20 % and 80 %. A large inner surface of the bed of media can be achieved by selecting either fine-sized media or media with a large pore volume. The large inner surface is required to ensure good sorption performance of the biofilter on the one hand and create the conditions necessary for a high microbial density on the other. Basically, all surfaces of the media particles, except for extremely small pores, are suitable to support microbial growth. Here, it should be noted that a finesized material causes a higher pressure drop than a coarse material. As the filter media inevitably undergoes decomposition and becomes progressively finer in the course of biofilter operation, the use of fine-sized media from the beginning results in a shorter service life. A good buffer capacity of the filter media helps avoid ph excursions. The various organic materials are subject to different decay rates. The more slowly a filter media decays, the smaller will be the pressure drop and the longer will be the service life. On the other hand, virtually inert (e.g. non-decaying) media are poor nutrient reservoirs for shutdown times and similar. Depending on its origin, the filter media exhibits a material-specific odour (without waste gas feed). Whenever possible, preference should be given to low-odour media. The nutrient salt demand (N, P and trace elements) of the microbial population should normally be supplied by the filter media. When treating waste gases containing N-bearing components (e.g. waste water treatment plants, composting facilities, livestock facilities etc.), this property of the filter media plays only a secondary role. In VOC control applications, by con15

16 trast, sufficient N and P levels of the filter media are crucial to proper biofilter operation and must be ensured at all times, if required by adding corresponding salts. 16

17 6 Results 6.1 Common air parameters Volume flow (average) Gas velocity [m/s] 8,5 Pipe diameter [mm] 230 Volume flow [m³/h] 1270 Filter volume [m³] 14 Filter space loading [m³/(m³h)] 90 The filter space loading denotes the volumetric waste gas flow related to the filter volume (m³/(m³h)). 6.2 VOC measurements with FID Date Crude gas [mg/m³] Clean gas [mg/m³] % 68% 54% 55% 51% 51% efficiency The overall elimination capacity of the biofilter shows an efficiency of > 50 % at an average filter space loading of 90 m³/(m³h). The graphs below show sample FID measurements. 17

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19 6.3 Odorimetry The measurements of odours were performed by Stuttgart University. The odour reduction efficiency characterizes the reduction of the odorant emission flow in terms of a process efficiency. Provided that the waste gas flow rate is not or only negligibly affected by the waste gas cleaning process, the odour reduction efficiency may also be calculated from the associated odorant concentrations according to the following equation: ݏ ݑݎ ݎݑ ݏ ݎݑ ߟ = ݎݑ ݏ ݎݑ Date Crude gas [OU/m³] Clean gas [OU/m³] efficiency 93% 94% 95% 98% 95% 95% The overall odour reduction efficiency is calculated to > 95% 7 Summary About half of the volatile organic components from the steel foundry and more than 95% of the odours can be degraded and removed biologically with an average filter space loading of 90 m³/(m³h). The overall VOC elimination capacity was not as high as expected, but this is due to the high amount of aromatic compounds from additives in the sand binders. 19