Figure 1. The control center at the KVA Linthgebiet plant. This is where all the processes taking place in the plant are monitored.

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1 Like a phoenix In a waste incineration plant such as the KVA Linthgebiet, located in Switzerland s Linth region, waste reaches the end of its life and then takes on a new one as raw material and electrical energy. A growing environmental awareness is leading us to separate and recycle more and more of our garbage. But what about the residual waste that can t be readily recycled? It ends up at waste incineration plants, such as the KVA Linthgebiet plant located in the Niederurnen municipality in the Swiss canton of Glarus. Here, it can be disposed of and any reusable components recovered from it. The strict environmental regulations that apply to waste incineration plants call for reliable, precise analysis techniques that inform operators of what the exhaust air and waste water contains, and in what quantities. 24 Customer application

2 High-tech waste recycling Walk into the control room of the KVA Linthgebiet plant and you d think you d stumbled on to the set of a science fiction movie. In front of a concave wall peppered with control monitors and LEDs is a semicircular desk with computer screens positioned on it (Figure 1). Of the 40 staff members who work at the plant, a handful are here in the cockpit manning the controls observing and deliberating, and monitoring the countless processes taking place in the plant. The KVA Linthgebiet plant disposes of municipal waste produced by the cantons of Glarus, Schwyz, and St. Gallen, as well as industrial waste. Incinerating waste is by no means its only task, however: it is also a recycling plant that recovers nonflammable components (both scrap iron and nonferrous metals) and generates current and district heating from the waste heat created by the incineration process. It s all in the mix A glass bay protruding from the control room, opposite the cockpit, houses another staff member in blue working gear. Here, this person has a view over the waste bunker where garbage is stored temporarily after it is delivered and operates a grab crane with a giant claw that he uses to transfer the waste to the furnace. He also mixes the garbage; this prevents contaminant levels reaching excessively high peaks, something which could put too much strain on the plant and result in lasting damage. If a load contains fluorinated plastics, for instance, hydrogen fluoride will be produced during incineration, followed by corrosive hydrofluoric acid in the subsequent wet flue gas purification process. While installations are able to withstand this acid in small quantities, they run the risk of damage if persistently high volumes of it are released. Figure 1. The control center at the KVA Linthgebiet plant. This is where all the processes taking place in the plant are monitored. INFORMATION

3 The plant is equipped with two furnace lines, where incineration takes place on hydraulically driven grates arranged in tiers. These transport the burning waste while also circulating it. The combustion process does not use any auxiliary fuels like oil or gas if the composition of the waste is right, it burns by itself. All that is used is air, blown in by fans to ensure that complete combustion can take place. The fl ue gas that is produced as a result of this reaches temperatures ranging between 950 and 1,000 C, and is used in the steam boiler to vaporize water. The steam drives two turbines, which the plant uses to generate approximately 80 gigawatt hours of electricity per year. Purified exhaust air: A step-by-step process The fl ue gas may contain a whole range of different con taminants, depending on what the waste is made up of; some examples of these are chlorides and heavy metals. Therefore, the gas is purifi ed in a number of steps before it is released into the environment. To start with, an electrostatic precipitator separates the solid particles. This is followed by fl ue gas scrubbing, in which the gas is fi rst cooled by spraying it with water which also washes out chlorides and heavy metals. This is referred to as the acidic stage of the fl ue gas scrubbing process. The gas is then desulfurized (in what is known as the alkaline stage) by adding caustic soda to the scrubbing water. At the end of the process, a wet electrostatic precipitator removes any water droplets that are present in aerosol form, thus «drying» the fl ue gas. Finally, the fl ue gas is conveyed into a denitrifi cation unit, where harmful nitrogen oxides are converted catalytically into water and molecular nitrogen (N 2, which makes up around 78% of the air we breathe); dioxins and furans are also destroyed at this point. The KVA Linthgebiet plant also purifi es its fl y ash. This ash is made up of two parts: one is the ash that is conveyed into the steam boiler together with the fl ue gas, while the other is the fi ne-grained ash that was separated in the electrostatic precipitator during fl ue gas purifi cation. The fl y ash scrubbing process uses the water from the three wet stages of fl ue gas purifi cation. The acidic quenching water dissolves the heavy metals out of the alkaline fl y ash. The bonus here is that the water is neutralized at the same time eliminating the need for neutralization agents during waste water treatment. The KVA Linthgebiet plant feeds its was Thorough treatment and inspection are 26 Customer application

4 A responsible attitude to people and the environment The waste gas is now ready to be released into the environment, while the scrubbed fly ash can be disposed of together with the slag. As the contaminants that were removed from the flue gas and fly ash are now dissolved in the scrubbing water, however, it is essential that the water undergoes thorough treatment and then inspection. This particular waste incineration plant feeds its waste water into the Linth Channel, a watercourse that flows between Lake Walen in the eastern foothills of the Swiss Alps and Lake Zurich. The majority of heavy metals are precipitated as hydroxide sludge in the plant s waste water treatment facility. Recycling companies are then able to recover a large proportion of the metals from this. In the plant, the next step is to remove heavy metals (like zinc, cadmium, and mercury) from the water using four ion exchangers that ensure that only trace amounts of these contaminants remain. Figure 2 (left). In the KVA Linthgebiet plant, nothing and nobody gets lost. Everything, right down to the lines and cables, has its place and is marked with signs. Direction signs point the way to the individual process steps (in this case, the sign is showing where acidic fly ash scrubbing takes place). This system is particularly beneficial in cases where problems have to be resolved in a hurry. Figure 3 (right). The ion exchanger unit (blue) is where heavy metals are bound from the scrubbing water used in flue gas purification and fly ash scrubbing. When the water leaves the ion exchangers, it only contains trace amounts of heavy metals. te water into a watercourse. absolutely essential. INFORMATION

5 Figure 4. A steam plume from the 100-meter chimney (left) can only be seen on a few days each year, under certain rare weather conditions. Snapshots are not enough The waste water that the plant produces is subject to the limit values imposed by Swiss water conservation regulations, and unannounced inspections by canton-level authorities are one way of ensuring that the plant remains compliant with these. Until recently, in-house inspections were also performed every month using atomic spectroscopy and photometry. However, there is no fi xed fi gure on the contaminant load that will be present in any given batch of purifi ed waste water: this varies according to factors such as the waste composition or the charge state of the ion exchangers that have to be regenerated regularly to remove the heavy metals bound in them. Therefore, the samples taken in these inspections only provided a snapshot not enough for either the operator or the authorities to know for sure that the values were remaining consistently below the limits. Improved monitoring thanks to online analysis This is what led the KVA Linthgebiet plant to begin running an online analysis instrument from Metrohm Applikon in December Every four hours, this measures concentrations of zinc, cadmium, lead, and copper in process waste water (Figure 5). Voltammetric determination is performed fully automatically using the ADI 2045VA. An alarm warns the plant staff when any of the four heavy metals is approaching a concentration that amounts to 80% of the limit value allowing ion exchanger regeneration to be introduced in good time and thus preventing limit values from being exceeded. Figure 5. The plant s ADI 2045VA from Metrohm Applikon is located one fl oor down from the ion exchangers, immediately beneath them. They feed the analyzer directly with samples. Analyses are performed fully automatically, and if the concentration of any of the heavy metals is approaching 80% of the limit value, the ADI 2045VA issues an alarm. 28 Customer application

6 Man and machine: A joint effort The determination of heavy metals in the plant s process waste water poses particular challenges for analysis. The task is to detect very low heavy metal contents in waste water samples whose composition is constantly changing, and where high salt concentrations are present but this is something that Metrohm s online analyzer is able to handle masterfully. Semicontinuous or continuous online analysis directly upstream of the receiving watercourse is the only way of responding rapidly to the variable operating states of the waste water treatment unit. And it goes without saying that this requires not only sophisticated analysis processes, but also a motivated team to put the necessary measures in place. Both sophisticated analysis processes and a motivated team are necessary to respond rapidly. Deputy plant manager Stefan Ringmann took us on a guided tour of the KVA Linthgebiet plant, where he has worked for nine years. Ringmann studied chemistry at Technische Universität München (Munich University of Technology). He fi rst came across the KVA Linthgebiet plant in 2000, when he was involved in an R&D project at the company Techform Engineering AG in Embrach (located in the canton of Zürich). In July 2005, he fi nally joined the staff at the plant, starting as the manager of the plant section dealing with fl ue gas purifi cation and waste water treatment. Despite rising to the role of deputy plant manager three years ago, he still likes to get back into a boiler suit from time to time and pitch in with his colleagues work. INFORMATION