Saving Water and Energy by Optimizing the Existing Plant

Cause

Saturated steam and cooling water are used for the production of plant components made of expanded polypropylene. The condensed steam and cooling water are returned to the cooling water basin after the production process. Due to the direct heating with steam, the condensation through cooling in the mold and the discharge together with the cooling water to the cooling water tank, there was no condensate return to the feed water tank, which resulted in high steam and feed water consumption. All the water for steam generation was taken from the municipal water network.
Due to the condensation of the steam and discharge into the cooling water basin, the supply of water to the cooling circuit was greater than the evaporation at the cooling towers. The excess cooling water was discharged into the sewage system. WEIL Wasseraufbereitung was commissioned to optimize both the water and heating circuits in order to save resources and costs.

Feed and cooling water treatment, heat recovery

After the inventory, WEIL developed a new concept. The following objectives were pursued:

Saving water:

• Recycling of excess cooling water
• Partial replacement of city water with well water

Energy saving:

• Recovery of waste heat from the cooling water
• Recycling of excess cooling water
• Optimization of boiler feed water treatment to reduce desalination losses (previously only softening, now desalination)

Installed:

• For water treatment for feed water: feed and mixed water tank with pressure boosting, reverse osmosis system with 22 m³/h with pre-filter, antiscalant dosing and downstream double softening
• Permeate tank, pure water pumping station
• For cooling water treatment: gravel filter and activated carbon filter, 8 m³/h each, with automatic backwash
• For heat recovery: 2 heat exchangers, insulated with automatically backwashable pre-filters and pumps for 2 cooling circuits for pre-heating the boiler feed water.
• Central switch cabinet with PLC control, process visualization via touch panel, completely installed and commissioned.

The following savings were achieved as a result of the measures:

Drinking water: 87,000 m³/year (78 %)
Waste water: 35,000 m³/year (53 %)
Natural gas: 5,000 MWh/year (7 %)
Water and waste water costs: € 165,000/year (37 %)
Energy costs: 185,000 €/year (6 %)
Investment costs: 400,000 euros/year
Operating costs: 37,000 euros/year
Amortization period: 16 months