In a waste water treatment plant sodium hydroxide, hydrochloric acid, heavy metal precipitation additives and flocculants are metered by N-P31 diaphragm pumps from Bran + Luebbe. The pumps’ reliability is ensured by the diaphragm control mechanism, which prevents damage to the diaphragm even under critical operating conditions.
Erzo is the authority responsible for public waste management in and around Oftringen, Switzerland, with facilities which include a waste water treatment plant and a power station that takes its heat source from garbage incineration. The incinerator with its associated power plant was built in 1970. It disposes of around 65,000 t of garbage annually from the local population of about 180,000. It was renovated in the early 1990s to comply with stricter environmental protection regulations. The waste water treatment plant, also recently updated, deals with both domestic and industrial waste water from neighbouring chemical and textile plants. Due to the chemical content of the water, sludge from the water treatment cannot be used as fertiliser and is completely incinerated, using a process which is unique to Erzo. Hot gas from the garbage incinerator at around 900 °C is passed through a rotary oven in the opposite direction to sludge which has had its water content reduced to about 25 % by a mechanical process. The sludge is first dried and then burnt, and the waste gas from the rotary oven is subsequently passed into the combustion chamber of the main incinerator to be reburnt. The rotary oven copes with around 30,000 t of sludge annually, both from the Erzo water treatment plant and also from surrounding plants. The advantages of this combination are:
- Lower cost: Operation, steam generation, NOx removal and exhaust gas clean-up are shared by the garbage and sludge incinerators
- The waste gas from the rotary oven contains nitrogenous decomposition products which help to reduce some of the oxides of nitrogen in the garbage incinerator and therefore reduce the consumption of feed material for the catalytic converter. When the sludge incinerator is in use, the consumption of ammonia for the catalytic converter is reduced by about half.
- The forced flow of hot gas from the rotary oven results in very efficient mixing of the combustion gases in the main incinerator and helps to increase the combustion efficiency and reduce corrosion.
One disadvantage of combining the sludge and garbage incineration is that sludge can only be burnt when the main incinerator is in use. This means that down-time has to be reduced to a minimum to avoid having to store the raw sludge, which would otherwise lead to excessive odour generation.
Twelve metering pumps
The plant‘s record of well over 8,000 operating hours per year is aided by the use of twelve Bran+Luebbe N-P31 type metering pumps. These pumps are used in four parts of the facility: Sodium hydroxide solution addition in the waste gas scrubber and for final effluent neutralisation, hydrochloric acid addition in waste water pre-treatment and final effluent neutralisation, heavy metal precipitation in waste water pre-treatment and flocculant addition for water pre-treatment. The diaphragm pumps have been in operation since 1995, to the complete satisfaction of the plant management. According to Thomas Mueller, General Manager of Erzo, the decision to replace the pumps originally installed by the plant construction company was a key factor in raising the plant’s availability, due to the frequent valve problems experienced with the previous pumps. The pumps‘ reliability is ensured by the diaphragm control mechanism, which prevents damage to the diaphragm even under critical operating conditions such as a blockage on the supply or delivery side. The Erzo pumps are also fitted with a diaphragm condition monitor which immediately signals any damage to the diaphragm. Even if this did happen, a hermetic seal is maintained so that neither the environment nor the plant operators can be contaminated by a leak.
The N-P31 pump is one of the Novados series, with a variable stroke of 0 to 20 mm. It can be fitted with either a plunger or a diaphragm pump head and has a maximum delivery of 0 to 720 l/h at a pressure of up to 500 bar. The P type can be combined with all other pump sizes in the Novados range. This flexibility is further enhanced by different ways of controlling and varying the flow rate, with manual, electric, electro-pneumatic or pneumatic stroke adjusters available. The speed of the pump drive motor can also be varied with a frequency controller. Novados pumps meet the requirements of the Machinery Directive 98/37/EC and Atex 94/9/EC. According to Theodor Kaufmann, the Erzo Maintenance Manager, one service day per month is sufficient to maintain all 12 pumps in 24-hour operation, resulting in a calculated availability of nearly 99 %.
cpp 435
Novados range
KVA Oftringen
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