PHE Control Valve Requirement

[jph90]

Hi guys,

Need some assistance on process design around a PHE I am looking to install. The HX serves to cool hot refined edible oil from 102 deg C to a nominal 45 deg C. The temperature of the outlet stream is not overly critical for any downstream processes, it is simply better for the quality of oil to store it at < 50 deg C following refining.

To achieve the cooling, the service fluid will be cooling water from the clients cooling tower. This circulates in supply/return headers at approx 60m3/hr, and i would be tapping off this to supply the required 12m3/hr to the HX for cooling. My question is - given that the temperature is not exactly critical (and it is acceptable for it to drop << 45 deg C as these are soft oils - will not go hard at low temps and viscosity is not an issue at low temps), is there a need for me to put a flow regulating control valve on the water supply line linked to a temperature transmitter on the oil outlet line? Wondering if this financial cost is necessary. What factors am i not considering? Is there a risk with feeding 60m3 unregulated to a PHE designed for ~12m3/hr?

 

[georgeverghese]

So you've got these 2 options
a)Install a restriction orifice on the supply or return line at this PHE sized for a flow of 12m3/hr at the lowest normal operating dp across the supply / return headers.
b)Install a TIC - TCV set to give you a constant 12m3/hr, where the TCV is sized in the same manner as in (a).

Option (a) would be okay if the client has no problems with your PHE taking up more than 12m3/hr when the operating dp is more than what what you've sized the RO for. If flow here could go as high as 60m3/hr, you'd obviously have to check if the piping and PHE can handle this flow safely. Erosion - corrosion may be also be a concern a this HX if you're using Cu-Ni as the material of construction for instance.

See if there is some way of recovering some of this heat, at an upstream feed-product preheat HX for example, before you finally cool it down to <50degC.

 

[EdStainless]

Or, install a combination of a fixed orifice and a thermal valve.
When the product is cold (because the cooling water is cold) you will only get water through the fixed orifice, and as the product warms up it the thermal valve will open and allow more cooling water flow through the HX.
This way you won't be cooling more than you really need to.
The valves don't use electronics, they are simply thermo-mechanical with a remote sense bulb.
We have found this a very effective method to get control of cooling.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[lilliput1]

I agree with EdStainless. Check out Watts self operating temperature regulator Powers # 11 Type WM regulator size 2" 3 way mixing type. Put balancing valve on the bypass leg. Make sure the valve regulates the flow of cooling tower water downstream of the heat exchanger so the cooling tower water in the heat exchanger will be close to pump discharge pressure so the cooling tower water will not boil at 215.6F (102C).

 

[jari001]

I'll also throw my hat in EdStainless' corner, I have worked with a lot of different machines that have thermal valves to ensure the lubricating oil stays under a certain temperature by allowing more cooling water flow. Low to no maintenance if you pick it right which is a nice plus.