Steam is an essential source of power for an industry especially when it is textile industry. Often it is seen in the factory the misuse of steam which is a direct waste of money! There is already pressure on the manufacturers that how to save money. Recovery of condensate and flash steam could save a huge amount for the industrialists and Forbes Marshall has a special solution for it.
Forbes Marshall is a leader in process efficiency and energy conservation for process industry for more than seven decades. Innovative solutions, knowledge, reliable products and global presence in more than 50 locations made them a trusted partner. They are the manufacturer of the widest range of steam engineering and control instrumentation products including – Steam Boilers (Gas/Oil/Solid Fuel fired), Exhaust Gas Boilers (EGB), Temperature & Pressure Control System, Condensate Recovery System, Steam Traps, Zero Leakage Piston Valves, Flow meters (for every application), almost everything related to steam and control instrumentation.
What is condensate?
Condensate is the result of steam transferring a portion of its heat energy, known as latent heat, to the product or equipment being heated. As steam loses heat and it turns back into the water, it contains 20% energy of the total steam.
This condensate water has a temperature equal to that of steam and it is basically distilled water, which is ideal for use as boiler feed water.
Recovering condensate reduces the fuel bill
Returning condensate to the boiler feed water tank raises the feed water temperature, improving the steam to fuel ratio. This cuts the fuel consumption thereby reducing the fuel bill.
Illustration: Consider, 1 kg of feed water to be converted to steam at 5 bar g.
| Table: As a rule of thumb, every 60C rise in feed water temperature saves 1% on the fuel bill. | |||
| Case-1 | Case-2 | ||
| A | Feed Water Temp. | 400C | 460C |
| B | Amount of energy in feed water | 40 kCal | 46 kCal |
| C | Steam at 5 bar g contains | 658 kCal/kg | |
| D | GCV of fuel
(Natural Gas) |
8700 kCal/m3 | |
| E | Amount of fuel required to produce steam,
(C-B)/D |
0.071 m3 | 0.070 m3 |
So, improvement of feed water temperature by recovering condensate from 30 to 90 deg C will give 10% fuel savings.
In textile industries, there is an opportunity to recover the maximum condensate water as boiler feed water where the makeup water requirement will be negligible.
Higher feed water temperature increases the boiler output
The capacity of a boiler is stated in ‘from & at’ rating which shows the amount of steam in kg/hr. which the boiler can create ‘from & at’ 100 deg C, at atmospheric pressure. Thus, the close the feed water temperature to 100 deg C, the closer the output generated to rated capacity.
Across most of the plants the feed water temperature is rarely maintained 100 deg C. Mostly it is ambient or slightly higher than ambient. This leads to a poor steam to fuel ratio and lowers the boiler capacity.
The following formula helps to calculate the steam output from the boiler-
Where, A = Specific Enthalpy of Evaporation at atmospheric pressure = 540 kCal/kg
B = Specific Enthalpy of Steam at operating pressure
C = Specific Enthalpy of Feed Water
Illustration:
| Feed Water Temperature | 40 deg C | 90 deg C |
| Max. steam generation capacity | 8,667 kg/hr. | 9,424 kg/hr. |
For a 10 ton/hr. capacity boiler, at 9 bar g operating pressure
Here, 500C rise in temperature in feed water increases the steam generation- 757 kg/hr.
Flash Steam contains almost 50% energy
Flash steam is low-pressure steam created when hot condensate water is released from a high pressure to a lower pressure within a steam system. It can be released through steam trap or blow through.
Recovering flash steam is as important as recovering condensate water. Although flash steam is very less (8~10%) in mass but it contains about 40~50% energy of the total condensate.
The following formula helps to calculate the flash steam-
% of Flash Steam = [(Enthalpy of Fluid * steam press. – Enthalpy of Fluid * Flash Press.) / (Enthalpy of Vapor * Steam Press. – Enthalpy of Fluid * Flash Press.)]
If, Condensate load is 3000 kg/hr.
Steam Pressure is 6 bar g
Flash Pressure is 0.5 bar g
% Flash Steam = 10% = 300 kg/hr.
Steam output = Boiler rating (kg/hr. x [A / (B-C)]
Flash steam should be recovered to the feed water tank or it can be used in somewhere else.
Other benefits are-
- Condensate water is free from TDS (total dissolve solid) and it reduces the requirement of blow-down thereby curtailing blow-down losses.
- Condensate does not need to undergo water treatment and thus saving water treatment cost.
- Recovering condensate reduces the cost for oxygen scavenging chemicals, since the improved temperature reduces the amount of dissolved oxygen mostly.
- Using Flash Condensing Deaerator Head helps to mix the condensate & flash steam with makeup water and reduce the oxygen and other gases from the feed water.
Forbes Marshall has a complete solution for condensate & flash steam recovery system with their Pressure Powered Package Pumping Unit (PPPPU) which is one of the most efficient ways of recovering condensate. It does not need any storage and electrical pump. More than 350 installations of Forbes Marshall Condensate Recovery Units are there in different textile industries in Bangladesh.
