BLOG: Power Perspectives

[#1]

Engine design and high temperature cooling systems
There are a few engines available in the market today that are designed for high temperature cooling systems. These cooling systems typically operate at temperatures of 127o C with the recovered jacket water heat used specifically for the purpose of generating steam. Higher temperature jacket water cooling systems of typically 110o C are also used in landfill or biogas applications where there are impurities in the gas and hence need to maintain elevated engine temperatures to hold the impurities in suspension in a gaseous state to keep them from condensing in the engine. These temperatures are usually higher than the boiling point of water under normal atmospheric pressures. These temperatures are only on the jacket water side on the cooling system.

Keeping the water in the engine in a liquid form at high temperatures
Another important issue to contend with is hot shutdown conditions. During this condition there is a tendency for the water near hot areas like turbo chargers to steam up and thus high temperatures are reached, as in steam form it can become super heated. It is important to maintain the cooling water at a pressure constantly above the boiling point even with the engine stopped.

This poses a real challenge for conventional cooling systems. The hot shutdowns and subsequent steaming has led to failures of turbo chargers and also led to corrosion in the cooling circuits. The conventional cooling system with expansion tank and pressure cap is supposedly pressurized too, but when the engine stops and cools the pressure turns down. Also the air in the expansion tank will cool faster than the water and can release the pressure faster. Hence there is a need for a better pressure regulating system that maintains cooling medium pressure at all times.

Common systems
There are many systems available in the market to do this function, but the most economical and commonly used is a bladder expansion tank system. The bladder expansion tank is an accumulator vessel with a bladder diaphragm inside. These expansion tanks provide a pneumatic cushion capable of continued operation without the loss of air into the system through absorption. This is possible because a flexible diaphragm (bladder) separates the water and air in the tank. The permanently sealed-in air cushion can be pre-charged to minimum system pressure to permit the smallest tank possible. This pressure balancing is what provides the required pressure of the water all the time.

Let us now examine the pressures needed for the various water temperatures. If water were to remain liquid at 101 deg C then a 7 psig pressure is needed in the system all the time. For a 110 deg C operation we need to charge to 14 psig. How do we achieve this in our cooling system design?

A typical diagram is given below:

• Here, the air is prefilled in the bladder tank to the required balancing pressure. In the case of 110 Deg C to 14 psig or 1 bar.
• Water is then filled into the cooling system to from the bottom most point using a pump and the system is fully bled of all air.
• The vent valve is then closed and the system is pressurized to 14 psig and the filling valve then closed.

 
This first provided the balanced cooling system. The sizing of the expansion tank is done so that when the water expands to the volume at 110 deg C the pressure in the system added does not exceed the maximum operating pressure of the system. The operating pressure should be such that the increase does not exceed 50% of the initial charge, i.e, if the initial charge pressure is 1bar the final operating pressures not to exceed 1.5 bar. Once this system is balanced the presence of positive pressure at all time keeps the system from steaming and any flashing will quickly dissolve back into the system. Another addition to the system can be a de-aeration chamber that will separate all the micro bubbles that are formed due to the pump churning action. This is usually located at the topmost point.


From the short discussion above you can appreciate that a properly engineered high temperature cooling system is paramount for a successful operating system. Care taken during the system design stage and installation will result in long engine life providing the owner / operator the expected return on investment.

• Have you ever used bladder expansion tank system? If so, what was your experience?
• Are there other considerations not mentioned above?
• Do you have experience with other types of systems? Please elaborate.
• Have you faced any problems in filling and pressurizing the system from your experience?
• How do we size the bladder expansion tank and the initial charge pressure?
• How do we prevent excess pressures from developing in the system?

Please share your thoughts by posting below.

[#2]

Have commissioned a number of systems with bladder type expansion tanks, in general if systems properly engineered minimum problems.

I'm not a fan of using engine driven pumps on high temp cooling systems, for two main reasons. First the design of a standard engine driven pump usually doesn't accomadate the higher temps and flow rates needed for a more complex cooling system.  Also an engine driven pump stops when the engine does, and many times the pump needs to run after the engine stops, especially after a fault to allow the entire system to cool properly.

Design a high temp system for coolant maintenance, standard glycol based coolants will likely not provide they properties needed by the system.  Assure that the coolant can be blown down, tested, and additives added safely in an operating system.  This means pot feeders, chemical injection system points, sample points, etc.  Don't assume piping contractor will install "as needed".

Make up systems are usually supplied from building water systems, assure new water makeup is properly filtered/conditioned to meet requirements.  Install a totalizer type flow meter, know how much water is going in for both fill and makeup, and keep track.

Thermostatic valves ususally have poor service life in higher temp systems, electric or air operated valves controlled by a temp controller or PLC usually provide better overall system performance and control, and can also be forced for startup and maintenace for cleaning/testing.

A closed system will need a PRV or relief valve, make sure the exhaust from this valve dumps in an area where no one can be hurt by a discharge of steam and/or hot water.

High point vents and low point drains are important in more complex systems, infortunately as more projects have greater cost pressures, the "nice to haves" get missed.  Don't assume an installer will put in vents and drains not shown in drawing, even if considered "good practise".

Assure a system audit is performed at completion during commissioning to assure system operates as expected and proper tuning of control parameters gets performed. Funny how a lot of systems don't work as expected when the ambient temp goes up or the system operates for a short time.

My 2 cents worth, Mike L.

[#3]

Mike,

Thanks for the valueable tips.. Yes we do agree that the system has to be properly Engineered to operate safely.

Understand your comments on the Engine driven pumps. The challenge we face is that most of the high temperature installations are in Bio Gas and landfill sites and it is better to keep the system operation as simple.. There is a preference to Engine driven pumps. By selecting proper oriifice we are able to get the flows we require. Further the challenge is when we have heat recovery. These are rare in landfill and Bio gas sites. When heat recovery in involved it is better to use Electic motor driven pumps for sure..

The Deareation chamber is usually provided with a PRV and vented to the top of the building. If properly filled and pressureized we have not seen steam vented even during hot shutdowns..

You can use 30 % concentration Dowtherm SR1 which, by itself raises the boiling point of water to 105 C at atmospheric pressure. This can be used upto 120 Deg C temp. For Higher temperatures there are other special organic coolants available.

The system is filled from the lowest point using a small pump and then pressurized to 1 bar.. The system has to be leak tested and sealed.. From our experience the use of make up water is almost nil.. When the pressure when cold drops in the system then we need to check the system..

Yes do agree with you that it is a challenge to audit and get it running given the cost pressures.. But overall the performance in the long run more than pays off for the initial troubles..

[#4]

Installation of a bladder type tank on a water system running at 101 degrees C is problematic in that the tanks are not rated for these temperatures.  This can be accomplished if the tank is plumbed in at a distance from the engine.  A minimum of 14 feet should be kept between the tank and engine in a horizontal plane so as to minimize the temperature of the coolant that may circulate in to the tank.  If space is an issue, a small radiator may be placed between the engine and bladder to lower the temperature that the tank may encounter.  A pressure gauge and temperature gauge should be Tee’d in to the tank bottom to monitor the status of the system and the tank.

[#5]

I have seen many a problem with ICEs at landfill sites, but high cooling temps have been somewhat minor problems. Lack of a good water sources (due to remote locations) undersized radiators, or dirty radiators have been more of a problem. I have operated and maintained applications at sites in California and NJ and the gas quality and complicated control systems have been more of a problem for my operators.

As far as engine driven equipment, I like the amount of engineering that CAT puts into their designs. They tend to match the equipment to the capacity of the engine systems (ie; lube oil pumps designed to keep a constant supply of oil flowing to the turbos on wind down). Many after market desings don't always take into consideration the factory engineering.

[#6]

Most of my expereince with high temperature cooling systems is in cogeneration applications.  Most of the biofuel applications I deal with, save a couple of wastewater DG that are also cogen, I can hardly get the operators to keep proper coolant additive in the engines, so for them simple is better anyway.

Some of the best systems I've seen are greenhouses and district heating in Northern Europe, very well done plants overall and well designed and very efficient cooling systems.

My high temp cooling system expereince started with G300 series ebuillent engines, and early on, many lessons learned from that.

I shy away from high temp systems using any form of glycol, too many issues with gylcol where I live and we have a large number of succesful projects using water based systems properly treated and maintained.  But different markets and regulatory environments make for differing solutions, no real one size fits all I think.

Mike L.

[#7]

Dear Garym1955,

You can use Amtrol Inc THERM-X-Trol ST 450 series Thermal exapansion tanks that are rated upto 115 Deg C .. The location of the tank is near the pump inlet and hence the temperature is aroung 104- 105 Deg C...

Pervin,

It would be a good idea to use the CAT premix for natural gas Engine coolant (NGEC) in places where water is a problem.. We have faced some sites here where the water is an issue and have used NGEC Premix... Once the cooling system is properly commissioned there is almost nil water loss as it is a closed circuit... Of course the best solution is where we can use good pure water as Mike suggests, but unfortunately is not possible..

Hope this will be of help

[#8]

I realy dont know 'bout cooling system...but thank you for this info for add my knowledge 'bout it.....

[#9]

Some of our projects Landfill or digester that we utilize exhaust waste heat recovery, doing this we have more restriction in the cooling system that the CAT JW head available.

 we sized a booster pump to maintain required flow and head. We control this pump to run after any shut down to control temperature overshoots.

 This is working extremely well for us. 

[#10]

Dear Colleagues,

The recent proposed Design for High Temperature Cooling Systems is very important for extending the operation life of the BIOGAS engines, which are used especially designed for Landfill and Biogas applications.

As stated previously, the main purpose from the proposed Topic for this discussion which is very relevant, it is to maintain and Keep the water in the engine in a liquid form, when we will operate the engine under HIGH temperature in order to extract to the exhaust the waste and residual of the biogas (NOT Natural) from the combustion chamber,

But what we have to take into consideration, it is the designed cooling system inside the engine, whether it is Combined coolant system (JW+AC/OC) or separate cooling system. But for the time being, i have never used and seen combined circuit, and for most Landfill and Biogas Applications, the coolant circuit for the biogas engines is designed as a separate coolant circuit JW, which means the cooling circuit for the air injected inside the combustion system will not be affected by this raise in temperature, otherwise, this elevation in temperature will lead to the dearating in the mechanical power of the engine and some negative technical affects to the operating life of the engine.

In addition to above recommendation, the Turbo Charger should support this elevation in temperature, otherwise, this increase in temperature (Especially the Exhaust Gas), this will lead to the defect and miss-operation in the engines.

Consequently, the Engine Oil or NGO, should be well considered for this operation temperation of the engine block, otherwise, the viscosity of the oil will be lost, and changing period will be short,

As for the proposed Pinping & Instrumentation Diagram, it is as Tipical Design, it could contain of more protection and reading instruments. But overall evaluation, it is the basic design, 

I hope above inputs are up to your satisfactions,

Wissam