Closed-loop cooling water system with plate heat exchanger for steel plants

01

Separate the closed loop from the open tower water

In a review of US iron and steel water use, Oak Ridge National Laboratory reports that once-through cooling has historically accounted for about 82% of total plant water use (80% for blast furnace–basic oxygen furnace plants and 93% for electric arc furnace plants), and that open-recirculating cooling towers and closed-recirculating systems are deployed to reduce water consumption. It states that melting, rolling and casting processes deploy closed-loop recirculating systems for indirect cooling of equipment, and counts heat exchangers, furnace shells and closed-loop cooling for finishing skids as non-contact water uses. [1]

The plate heat exchanger is the boundary between the two loops. Kelvion describes its gasketed plate heat exchanger range as covering connection sizes from DN25 to DN500 (1 to 20 inches), with plate materials including titanium-palladium and alloys such as C-276 and 254 SMO; its product filter lists design pressures up to 29 bar for the NT series, 31 bar for NX and 33 bar for NP, and up to 64 bar(g) on the welded side of its semi-welded HPL series. [3]

Editorial note: choose the plate material for the dirtier, more corrosive side, which is the open tower water, and ask for the approach temperature between the closed-loop outlet and the tower water inlet, since it sets how cool the closed loop can run on a hot day.

Give the supplier each consumer's heat load and required supply temperature, the closed-loop flow and return temperature, available tower water temperature and quality, pressure limits, standby pump requirement, plate material, and the space for the skid.

02

Manage the cooling tower water: cycles and blowdown

The US Department of Energy's Federal Energy Management Program explains that water leaves a cooling tower by evaporation, drift and blowdown, so make-up equals evaporation plus blowdown plus drift, and that cycles of concentration, the ratio of dissolved solids in blowdown to make-up, is a key operating parameter. [2]

FEMP states that systems operate at two to four cycles while six or more may be possible, and that increasing cycles from three to six reduces make-up water by 20% and blowdown by 50%. It recommends a conductivity controller to control blowdown automatically, set with a water treatment specialist. [2] Editorial calculation: ignoring drift, make-up ≈ evaporation × cycles ÷ (cycles − 1); at 100 m³/h evaporation that is 150 m³/h at three cycles and 120 m³/h at six, a 20% reduction, consistent with FEMP's figure.

ORNL lists drift eliminators, conductivity-controlled water supply, and variable frequency drives on tower fans and pumps among water efficiency measures reported for steel plants. [1]

03

Build the pump and exchanger skid

Editorial note: the sources reviewed describe the exchanger and the tower water in detail but not a standard skid, so define the skid contents in the enquiry: pumps and standby, exchanger, filters, expansion and make-up, instruments and controls. [3] [2]

Kelvion describes gasketed exchangers as tailor-made for small to very large flows and lists gasket materials chosen for temperature, chemical resistance or food approval. [3] Editorial note: ask the supplier for pump curves at the design flow, the pressure drop across the exchanger and filters, the strainer mesh, and the corrosion inhibitor and biocide programme for both loops.

04

Chiller or non-refrigerated loop, skid contents and exchanger sizing to confirm per quote

Ask each supplier whether the quote is a refrigerated chiller or a non-refrigerated closed loop, which items are in the skid, and how the exchanger was sized.

05

Closed loop, plate exchanger, pumps, cooling tower, blowdown control and filters

06

Heat load, loop flows, exchanger design pressure and plate material for a steel-plant cooling loop

Heat load and supply and return temperatures come from your consumers; the published values here are exchanger limits from one Kelvion series, such as design pressure up to 29 bar. [3]

07

Send the heat load, water and layout data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Consumers: [equipment; heat load; supply temperature each]
Closed loop: [flow; supply and return temperature; water treatment]
Tower water: [temperature; quality; cycles target]
Exchanger: [approach; plate and gasket material; design pressure]
Pumps: [duty and standby; head]
Controls: [instruments; conductivity blowdown]
Layout: [skid size; connections]

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