Condensate Return Systems provide excellent opportunities for substantial savings in energy, water and chemical costs.
Improvements to a condensate return system often are also beneficial from the perspective of production efficiencies.
The cost saving due to returning the water content of condensate to the boiler as feedwater requires no great cost benefit analysis. The unit costs of boiler water, treatment chemicals and effluent charges are usually well known in a plant, as is the energy cost to provide both sensible and latent heat to the feedwater in the boiler.
Usually less well documented is the loss due to flash steam, occuring as a result of condensate pressure drop.
Primary pressure drop in steam condensate systems is usually across the steam trap of a particular heat exchanger or other steam-heated equipment.
Take the example of a typical Cardboard Corrugator, and assume a supply pressure to the steam-heated rolls of 10 bar g and a condensate return line pressure of 0.5 bar g. The resulting flash steam percentage can be read off the graph as about 14%. Assuming a steam usage for this particular steam-heated roll of 100 kg/h, the flash steam would amount to 14 kg/h.
If a dual-pressure steam system is used, with the hot plate section supplied with 3 - 4 bar g steam, the amount of flash steam from this roll would be about halved to 7 - 8% or 7 - 8 kg/h.
Basic Options for Flash Steam Utilisation:
1. Reduce amount of flash steam by reducing the steam pressure in a process. This also has the added benefit of increased latent heat value corresponding to lower steam pressures, resulting in extra steam cost savings.
2. Install a Flash Vessel and use the flash steam for pre-heating a process medium using lower pressure steam. Paper machines and Corrugators are obvious candidates, as are many processes in the petrochemical and food industries. Pre-heating of boiler feedwater and combustion air are almost always available as possible heat sinks.
3. Use high pressure condensate return to reduce the amount of flash steam formation. This can result in dramatic energy savings in systems where a minimum pressure differential exists at all times. Usually this applies to systems where the steam pressure remains essentially constant. Condensate can then be collected in a pressure vessel and pumped directly back to the boiler.
Alternatively,where the steam supply pressure modulates (for instance by means of temperature or pressure regulating valves), a deaerator can be a useful "condensate pressure controller".
In a deaerator, flash steam directly replaces live steam usage for removal of O2 and CO2 from boiler feedwater.
Our standard deaerators normally operate at 0.5 to 1 bar g, in order to achieve the minimum temperature needed for proper deaeration. However, they can be purpose built for any higher pressure if this is cost-efficient from the aspect of maximum flash steam utilisation.
Another benefit of pressurised condensate returns, especially when a deaerator is employed, is the utilisation of the inevitable live steam losses through steam traps and other equipment.
SYSTEM DESCRIPTION
A boiler supplies 10 bar g steam to a Corrugator.
The boiler plant incorporates a Flue Gas Heat Recovery System A, as well as a Continuous Blowdown Heat Recovery System B, both of which serve to pre-heat cold make-up water.
The deaerator operates with 0.5 bar g steam supply. Its primary function is the mechanical deaeration of feed water to minimise the cost of oxygen scavenging chemicals. The deaerator also serves as an important recipient of pressurised condensate and flash steam, as well as live steam losses from steam traps. This secondary function alone can often justify the cost of a deaerator.
A Steam Dryer is installed in the 10 bar g steam main close to the boiler, to ensure highest heat transfer efficiency for the process.
The corrugator rolls are fed with 10 bar steam, depicted as SectionC. Steam pressure to the rolls is essentially constant.
A Pressure Reducing Valve drops 10 bar g steam to 4 bar g for the Hot Plate Section D.
Condensate from the Rolls Section C is expanded in a Flash Vessel. Flash steam is piped into the 4 bar g Section D steam supply, where it replaces an equivalent amount of live steam. For this example, about 7% of condensate flashes from 10 bar g to 4 bar g.
Remaining condensate from Section C flows by differential pressure to the deaerator.
The Hot Plate Section D is equipped with individual pressure controls for temperature adjustment. Therefore the pressure differential may at times be insufficient to transport condensate from Section D back to the deaerator.
A Thermgard LIFTMASTER condensate pump is employed to ensure automatic condensate removal from the Hot Plate Section D back to the deaerator. The pump is steam-activated on demand, and requires no electrical power or control. Steam consumption is about 1 kg per 1000 kg condensate pumped.
ADVANTAGES OF CLOSED LOOP CONDENSATE RETURN:
Minimal make-up water requirement = substantial water and treatment chemical cost savings.
Oxygen-scavenging chemical costs drastically reduced.
Greatly reduced blowdown requirements = lower water, chemical and energy costs.
Boiler fuel cost savings 10 - 15 % due to utilisation of flash steam.
Water and fuel cost savings due to utilisation of live steam losses from steam traps etc
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Improvements to a condensate return system often are also beneficial from the perspective of production efficiencies.
The cost saving due to returning the water content of condensate to the boiler as feedwater requires no great cost benefit analysis. The unit costs of boiler water, treatment chemicals and effluent charges are usually well known in a plant, as is the energy cost to provide both sensible and latent heat to the feedwater in the boiler.
Usually less well documented is the loss due to flash steam, occuring as a result of condensate pressure drop.
Primary pressure drop in steam condensate systems is usually across the steam trap of a particular heat exchanger or other steam-heated equipment.
Take the example of a typical Cardboard Corrugator, and assume a supply pressure to the steam-heated rolls of 10 bar g and a condensate return line pressure of 0.5 bar g. The resulting flash steam percentage can be read off the graph as about 14%. Assuming a steam usage for this particular steam-heated roll of 100 kg/h, the flash steam would amount to 14 kg/h.
If a dual-pressure steam system is used, with the hot plate section supplied with 3 - 4 bar g steam, the amount of flash steam from this roll would be about halved to 7 - 8% or 7 - 8 kg/h.
Basic Options for Flash Steam Utilisation:
1. Reduce amount of flash steam by reducing the steam pressure in a process. This also has the added benefit of increased latent heat value corresponding to lower steam pressures, resulting in extra steam cost savings.
2. Install a Flash Vessel and use the flash steam for pre-heating a process medium using lower pressure steam. Paper machines and Corrugators are obvious candidates, as are many processes in the petrochemical and food industries. Pre-heating of boiler feedwater and combustion air are almost always available as possible heat sinks.
3. Use high pressure condensate return to reduce the amount of flash steam formation. This can result in dramatic energy savings in systems where a minimum pressure differential exists at all times. Usually this applies to systems where the steam pressure remains essentially constant. Condensate can then be collected in a pressure vessel and pumped directly back to the boiler.
Alternatively,where the steam supply pressure modulates (for instance by means of temperature or pressure regulating valves), a deaerator can be a useful "condensate pressure controller".
In a deaerator, flash steam directly replaces live steam usage for removal of O2 and CO2 from boiler feedwater.
Our standard deaerators normally operate at 0.5 to 1 bar g, in order to achieve the minimum temperature needed for proper deaeration. However, they can be purpose built for any higher pressure if this is cost-efficient from the aspect of maximum flash steam utilisation.
Another benefit of pressurised condensate returns, especially when a deaerator is employed, is the utilisation of the inevitable live steam losses through steam traps and other equipment.
A boiler supplies 10 bar g steam to a Corrugator.
The boiler plant incorporates a Flue Gas Heat Recovery System A, as well as a Continuous Blowdown Heat Recovery System B, both of which serve to pre-heat cold make-up water.
The deaerator operates with 0.5 bar g steam supply. Its primary function is the mechanical deaeration of feed water to minimise the cost of oxygen scavenging chemicals. The deaerator also serves as an important recipient of pressurised condensate and flash steam, as well as live steam losses from steam traps. This secondary function alone can often justify the cost of a deaerator.
A Steam Dryer is installed in the 10 bar g steam main close to the boiler, to ensure highest heat transfer efficiency for the process.
The corrugator rolls are fed with 10 bar steam, depicted as SectionC. Steam pressure to the rolls is essentially constant.
A Pressure Reducing Valve drops 10 bar g steam to 4 bar g for the Hot Plate Section D.
Condensate from the Rolls Section C is expanded in a Flash Vessel. Flash steam is piped into the 4 bar g Section D steam supply, where it replaces an equivalent amount of live steam. For this example, about 7% of condensate flashes from 10 bar g to 4 bar g.
Remaining condensate from Section C flows by differential pressure to the deaerator.
The Hot Plate Section D is equipped with individual pressure controls for temperature adjustment. Therefore the pressure differential may at times be insufficient to transport condensate from Section D back to the deaerator.
A Thermgard LIFTMASTER condensate pump is employed to ensure automatic condensate removal from the Hot Plate Section D back to the deaerator. The pump is steam-activated on demand, and requires no electrical power or control. Steam consumption is about 1 kg per 1000 kg condensate pumped.
ADVANTAGES OF CLOSED LOOP CONDENSATE RETURN:
Minimal make-up water requirement = substantial water and treatment chemical cost savings.
Oxygen-scavenging chemical costs drastically reduced.
Greatly reduced blowdown requirements = lower water, chemical and energy costs.
Boiler fuel cost savings 10 - 15 % due to utilisation of flash steam.
Water and fuel cost savings due to utilisation of live steam losses from steam traps etc
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