Direct Steam Injection vs Indirect Steam Injection
Direct Steam Injection vs Indirect Steam Injection
(OP)
I have a project for a process equipment which is using direct steam injection (motorized valve use to inject steam to water supply pipe) to produce hot water. I will convert it to indirect type using plate heat exchanger and steam as heating medium to produce hot water. Is my project will reduce energy cost?
Note: Condensate will be returned using steam trap on indirect steam injection
Thanks,
Benedict
Note: Condensate will be returned using steam trap on indirect steam injection
Thanks,
Benedict





RE: Direct Steam Injection vs Indirect Steam Injection
RE: Direct Steam Injection vs Indirect Steam Injection
1. You'll need a pump on the water side.
2. The surface of the heat exchanger, pump, and extra piping will lose heat to the surroundings. If you are putting your exchanger directly into the water flow rather than pumping in a loop, you will add pressure drop. The pump supplying the water flow will have to raise its pressure to maintain the same flow.
3. You'll have to pump the condensate up to boiler pressure to return it, and you aren't doing that now.
Wait and see what the real thermo experts have to say, though.
Best to you,
Goober Dave
Haven't see the forum policies? Do so now: Forum Policies
RE: Direct Steam Injection vs Indirect Steam Injection
Currently with direct steam injection all the heat of the steam is used in heating up the cold water to the desired temperature. With an exchanger because you have a hot condensate stream being trapped off, you will use more steam to compensate for the enthalphy exiting with the condensate in heating up the cold water to the final temperature. The savings from recovering condensate in terms of chemical treating costs can be estimated from your current operation. The energy value of that hot condensate depends on your system. If for example you have a surplus of low pressure steam, the energy value of that hot condensate might be little or none. However, if you have to let down steam to heat up the additional cold BFW, there might be a significant energy savings.
Or it might just be the end of a long day and my brain isn't working
RE: Direct Steam Injection vs Indirect Steam Injection
You will actually need a little more steam and there will be pumping losses.
In terms of raw efficiency you can't beat direct injection.
= = = = = = = = = = = = = = = = = = = =
Plymouth Tube
RE: Direct Steam Injection vs Indirect Steam Injection
In a direct steam injection process you exploit not only the latent heat, but also part of the sensible heat of condensed steam, whilst in an indirect process you trap and discharge hot condensate.
Moreover in an indirect process you introduce further thermal resistances which reduces the heat transfer efficiency.
On the other hand the hot condensate pumped back to feed your boiler reduces the need of fresh makeup water and the need of raising its temperature (feeding a boiler with fresh cold water is definitely not a good way to go).
One last point, though this is probably not your case as the direct steam injection had been already adopted for your specific application. There are applications were the direct contact between the heating stream and the fluid to be heated is not allowed and so the only option is an indirect process.
RE: Direct Steam Injection vs Indirect Steam Injection
Diret heating is the best use of the heat available. Indirect heating is the best use of the water available.
With direct heat, you have to treat and heat the make-up water and that has a cost too. (You do treat the boiler make-up water don't you?)
rmw
RE: Direct Steam Injection vs Indirect Steam Injection