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Hot saving potentials in the cooling water supply of a chemical company
Many chemical processes require a constant operating temperature. This can be provided by complex cooling water systems with heat exchangers, for example, as is the case at a large international chemicals group. Experts from SES System Efficiency Service were commissioned to investigate one of these energy-intensive systems in detail, uncover potentials for optimisation and find ways of tapping into them.
Many chemical processes require a constant operating temperature. This can be provided by complex cooling water systems with heat exchangers, for example, as is the case at a large international chemicals group. Experts from SES System Efficiency Service were commissioned to investigate one of these energy-intensive systems in detail, uncover potentials for optimisation and find ways of tapping into them.
Optimisation
A system that has grown over the years, spanning several buildings and floors
The cooling water supply system to be investigated had grown historically and is highly complex: In the supply line, five fixed speed pumps distribute the cooling water over three risers leading to several heat exchangers, with all of the equipment being installed in several buildings and on different floors. In summer, three of the five pumps are in operation; in winter only two. Upstream of the last consumer installations, at a height of 15 m, two continuous-duty pressure booster pumps are in action. Some of the consumers are fitted with a control valve; some are not.
The SES System Efficiency Service experts were commissioned to analyse the system in depth and to identify optimisation opportunities.
First, the goals of the analysis were defined:
- Determine the operating data of the seven pumps installed
- Create a pump characteristic curve incl. the current operating point/range
- Check the power input incl. efficiency
- Analyse the overall system and identify the overall efficiency
- Recommend actions for operation to be efficient and reliable in the future
KSB's energy efficiency experts conducted various measurements over a period of six days. They analysed the inlet pressure and discharge pressure of the pumps, the flow rates and power input as well as the pressure and temperature differences. Summer and winter operation were simulated. The results revealed the following:
Regarding the condition of the five WTS A 250 36 cooling water pumps (fixed speed, control by throttling) from Halberg
- During normal operation (summer) the pumps are running at overload.
- Overload and wear have already decreased the pumps' efficiency to approx. 55 %.
- In winter, the pumps are operated outside the permissible operating range.
Regarding the condition of the two Etanorm 125-250 pressure booster pumps (fixed speed, control by throttling) from KSB
- During normal operation (summer), the pumps are operated outside their permissible operating range.
- The pressure booster pumps do not increase the pressure during normal operation.
- Overload and wear have reduced pump efficiency to a maximum of 25 %.
Based on an internal electricity price of 5 ct/kWh and the previous operating parameters, the energy costs equal € 198,500 per year.
Data analysis revealed that the cooling water pumps to be investigated are operated at a markedly reduced efficiency.
The solution:
Replacing the pumps with new, more efficient models
KSB's experts prepared the following optimisation concept for the customer:
- Replacing all five pumps with pumps of the type Etanorm E 350-300-375 driven by 160 kW motors in flameproof enclosure, for variable-speed operation
- Installing five frequency inverters and a higher-level, load-dependent control system
- Installing a bypass around the pressure booster pumps as these are currently not required in normal operation
KSB's pressure booster pump of the type Etanorm 125-250 without frequency inverter is also running at reduced efficiency.
The result:
An energy-efficient, reliable system with reduced CO₂ emissions
The customer decided to implement the recommendations with the following benefits:
- Higher operating reliability with optimised materials
- Pump operation in permissible operating range at best possible efficiency
- Current flow rates will also be met in the future
- Flexible adjustment with variable speed pumps
- Similar pump characteristics enabled the upgrade to be implemented step by step
Savings compared to current operation: approx. 66.2 %, equalling € 133,300 per year
A comparison of life cycle costs shows: Despite the rather low energy price of 5 ct/kWh the investment costs are paid back within less than 3 years.
Figures I Data I Facts
Application: chemical industry
Project year: 2021
Scope: Investigating the pump system for cooling water supply. Installing 5 variable speed process pumps incl. optimised control technology. Shutting down two pressure booster pumps.
Previous situation | Optimised situation | |
Drive rating [kW] | 5 x 190, fixed speed | 5 x 160, variable speed |
Energy savings [%] | - | 66.2 |
Energy input [kWh/a] | 3,970,000 | 1,343,000 |
| Emissions [t CO₂/a]1 | 1,453 | 492 |
| Electricity price [€/MWh] | 50 | 50 |
Payback period [years] | - | 2.8 |
1 Based on a CO₂ emission factor of 366 g/kWh for power consumption in Germany
