Chemical-dosing systems at two U.S. based locations

Preparing the ground

Cooling and boiler water of power plants on the premises of chemical factories must be conditioned in a similar way to the water of large-scale power plants. This is an important basis for an efficient energy supply when manufacturing substances such as fertilisers. During the water treatment, various chemicals are added by special dosing stations. Designing such dosing equipment for the U.S. market turns out to be challenging, though.

MPT of Rodgau (Germany) was commissioned by Thyssen Krupp Industrial Solutions to furnish two U.S. based chemical plants operated by CF Industries with
27 dosing systems. Four dosing stations for oxygen scavenger, amine, phosphate and caustic were erected in Donaldsonville, Louisiana. Two dosing stations for each of seven other fluids were also installed there: surfactant, dispersing agent, corrosion inhibitor, sodium bromide, sodium hypochlorite, sulphuric acid and sodium hydroxide. One dosing system for each of the following media was shipped to Port Neal, Iowa: oxygen scavenger, ammonium hydroxide, sodium hypochlorite, corrosion inhibitor, dispersing agent, sodium bromide, non-oxidising biocide, sulphuric acid and sodium hydroxide.

Each of these stations basically consists of a storage tank, which is filled by means of gravity or compressed air, as well as two or more dosing pumps. The pumps for each dosing line are embedded in a redundancy concept: if one pump fails, the other one cuts in automatically.

Project requirements

American dosing pumps were installed in this project in order to permit maintenance within the U.S.A. The entire electrical equipment – such as motors, transmitters and switches – had to be U.S.-certified either by FM Global, a mutual insurance company located in Rhode Island, or by UL, the Illinois based safety consultant. The pressure gauges and flow indicators likewise had to be appropriately designed. Since 18 dosing systems were delivered to Donaldsonville alone, the operator wanted them to have a uniform design to ensure ease of installation, operation and maintenance. Finally, they had to be sufficiently robust to last for many years.America uses Imperial rather than metric units, meaning that all tanks and flanges had to be secured with Imperial size bolts. Furthermore, the dimensions of the dosing stations in all general arrangement drawings are in feet and inches while the weights are in pounds. These dimensions and weights formed the basis for the customer’s wind load calculation. The component parts were coated according to a specification which only applied to the pumps and motors. Although not specified in the contract, MPT coated the polyvinyl chloride and polypropylene piping for the Donaldsonville systems with a special UV protectant because they were intended for outdoor use.

Standards are of particular interest in the U.S.: thus, for example, API 675 for positive displacement pumps and the NEMA standard for motors had to be adhered to. NEMA (National Electrical Manufacturers Association) also publishes standards for product safety information such as symbols, warning messages in product manuals and warning labels attached to the product itself. In America, product safety information must fulfil strict comprehensibility requirements. Whereas ISO symbols cannot be understood without being learned, a U.S. symbol depicts a risk of injury very drastically in order to maximise the deterrent effect. In addition, the black-and-white presentation makes for a better contrast. Last but not least, U.S. symbols are larger than their ISO counterparts as they are not framed by a warning triangle or a blue circle.

Coping with problems

For MPT, the size of some of the tanks turned out to be challenging as regards packing and transport. To keep logistics costs as low as possible, extra-large tanks were ordered, delivered and installed directly in the U.S.A. solution had to be found to make this relatively simple in spite of the separate delivery. The pump group was therefore connected to the appropriate tank with flexible tubing, easily compensating the dimensional deviations which can occur during assembly.

Component parts subject to maintenance – i. e. safety valves and the above-mentioned dosing pumps – can be serviced and repaired by local businesses, making any maintenance work much easier for the operating company.

The thoroughly prepared, comprehensive and detailed sets of documentation – including piping and instrumentation diagrams, general arrangement drawings and assembly and operating instructions – smoothed the transition to these complex process facilities.

Throughout the project, MPT’s great flexibility as system manufacturer proved to be particularly helpful for the client: a company-wide flat hierarchy and quick decisions paved the way for comprehensive customer support, enabling prompt answers to the questions that always arise when installing and commissioning such systems.

Online search: cpp0317mpt

Author : Sven Briol

Project Manager,


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