1. Process Heating – Temperature Stability Under Dynamic Flow Rates Direct Steam Injection for Sustainability
David Degelau
Hydro-Thermal Corp
Certified Steam System Specialist

2. Presentation Summary Industrial heating methods
Direct steam injection (DSI) basics
Inherent properties for sustainability
Case Studies -
Thanks to all of you for the opportunity to speak with you regarding direct steam injection this afternoon. I’ll begin with presenting the basics of direct verses indirect heating using conventional sludge heat exchangers as a reference point for presenting the benefits of DSI.
I’ll review internal modulation verses external modulation.
Cover the advantages of DSI using hot water heat exchangers as a reference point.
I’ll show various digestion heating flow schemes using DSI.
Present typical DSI heater dimensions and installations.
Followed by specific digester benefits that can be realized with DSI and conclude with a summary and questions and answers.

3. Industrial Heating Methods Direct and Indirect Steam Heating

4. Indirect or Direct Heating
Steam in
Cold Liquid In
Warm out
This chapter discusses the difference between direct and indirect steam heating of fluids.
Indirect heating is most commonly seen in the form of plate & frame or shell & tube heat exchangers.
Heat exchangers inefficiently transfer heat through a membrane. This results in only ~ 83% of the heat energy transferred to the process fluid while the remaining energy is discharged in the form of condensate.
DSI uses 100% of the steam’s heat energy by adding steam directly to the process fluid.
The primary benefits of Direct contact heating vs Indirect include
Energy savings of 25% or more.
Precise and instantaneous temperature control is possible to within 1 degree F
No production floor space is required
Reduces maintenance via self cleaning and elimination of a condensate return system
Cold liquid in
Hot condensate out

5. Direct Fluid Heating - Sparging
Oldest method of direct steam injection
Very inefficient
Prone to tank failure
Limited temperature control
High maintenance costs
As we have already discussed the difference between direct and indirect heating, I’d like to discuss other forms of direct steam injection.
Sparging is the oldest, simplest and least complicated technique for mixing steam with liquid or slurry to effect heating. It is basically injecting steam directly into a fluid filled tank. Though considered simple and inexpensive, sparging is very inefficient and the operation invariably results in:
Poor heat injection economics due to steam energy escaping from vessels without condensing.
Equipment failure (both vessel and sparger pipes) due to the vibration associated with steam hammer when not operated within their narrow design envelope.
Usually less than satisfactory on/off process control. A sparger is the least controllable DSI heating method.
High maintenance costs for tanks, sensors and piping are the norm if the equipment operates outside the design parameters.

6. Common Sparging Problems
Steam Hammer
Steam bubbles present in pipe
Bubbles combine and grow
Bubbles contact cool pipe wall and collapse
Water rushes into void at high velocity
Overheated zone around sparge nozzle
Steam bubbles in pipe may damage tank
Steam bubbles may escape into atmosphere
Start with sparging nozzle, discuss how they are supposed to work. Breaking up steam into relatively small bubbles.
Bubbles are still relatively large.
As temperature demand drops, pressure drops, potentially causing instability.
Bubbles can be present if liquid is hot, or not miscible with steam
Startups can be rough since liquid can back up to steam valve.
Tanks:
Overheated Zone around nozzle
As tank heats, Heat transfer slows
Steam may escape to atmosphere
Agitation very important

7. Direct Fluid Heating – Mixing Tees
Very high maintenance
Prone to scaling and fouling
Steam hammer common
Potentially very dangerous
Limited temperature control
Mixing Ts combine separate streams of steam and cold water to produce heated water. Because accurate temperature control is difficult to maintain with this method, mixing Ts are not the best choice for process fluids. When used for water, mixing tees are prone to scaling, fouling and excessive hammer. Due to the plugging, scaling and fouling, mixing tees can also be very dangerous if live steam flows through the hoses.

8. Direct Fluid Heating – Sparge TubeTM
Perforated tube sparger
Requires external steam control valve
Very high maintenance
Prone to scaling and fouling
Steam hammer common
Limited temperature control due to external control
Internal spring prone to breakage
Commonly known as the Pick heater, the modulatable sparger tube (MST) heater consists of a spring controlled, variable-injection sparger tube inside a cast process flow body. In response to a temperature sensor, the external flow control valve modulates the steam to a spring-loaded piston. MST heaters work reasonably well on clear liquids and some low solids solutions but are subject to severe clogging and steam hammer if frequent maintenance is not performed. In typical water heating applications, these devices typically require monthly tear down and acid bath cleaning. Since the steam flow is dependent upon a spring loaded valve, accurate temperature control is difficult once the spring begins to wear. Spring failure is a common issue with this type of heater.

9. Direct Steam Injection vs. Heat Exchangers

10. Contrast: Heat Exchanger vs. DSI
Indirect vs. Direct
Indirect = heat transfer only; no fluid mixing
Steam in
(Hot)
Warm
out
Cold Liquid in
Hot Condensate

11. DSI Advantages
Rapid and uniform heating—important in starches and food products
Can heat highly viscous fluids
Handles fluids that are difficult to heat—avoids “bake-on”; abrasive slurries
Compact footprint
Minimizes plugging and fouling
Rapid response time

12. Energy Losses in the Heating Process
Water
Treatment
Makeup water
Process Fluid HX
Trap system
Boiler
Blow Down losses
Condensate losses
Stack losses
Flash losses
Heat loss
Steam
Energy losses in a typical system
Stack losses: 10-30% of energy input
Blow down losses – 5-10% of boiler output
Condensate losses due to leaks or non functioning trap systems – up to 10% of energy input
Flash losses – 5-10% depending on system pressures as hot condensate is reduced in pressure
Condensate heat losses < 2% of energy input
Pump power

13. Maintenance – Steam Systems
Water
Treatment
Slurry HX
Trap system
Boiler
Condensate return
Blow Down
Makeup water
All Boilers require water treatment systems to produce soft treated water. Salt, chemicals and water quality must be added and monitored.
A portion of the boiler contents must be purged periodically to remove sediment and maintain efficiencies
Typically 5-10% of the output volume is discharged in this manner. In DSI systems output is usually 2-5% less.
Steam based heat exchangers have a boiler and condensate return system that must be maintained. These systems drop the water pressure and temperature below the boiling point.
They are often prone to failure due to plugging and scale buildup.
A well-maintained steam system will typically experience a 10% trap failure in a 1-year period. This can translate into significant
losses to the system.
System debris, improper sizing, and improper application are common causes of steam trap failure. Steam traps
can fail in different modes. Two main failure modes result in significant economic impact. A
failed-open steam trap allows “live” steam to discharge from the system, a steam leak. Steam
traps may also fail closed, which allows condensate to backup into the equipment drained by the
trap. If this is a process heat exchanger, the product will not receive the energy intended. Water
hammer can also result, which can damage piping components.
* Steam Survey, 2002 Greg Harrell, Ph.D., P.E. US Dept. of Energy

14. Internal Modulation Steam Inlet Steam Velocity ~1500 ft/sec
Full Steam Pressure
(Psteam)
High Velocity
Steam Jet
Steam Nozzle
Combining tube
Stem / Plug
Hot Liquid Discharge
Steam Inlet
Liquid Inlet
Steam Velocity
~1500 ft/sec
The hydro heater uses patented internal steam modulation bringing full steam pressure to point of injection.
This allows 0-100% adjustment control with complete stability. Other advantages include sonic velocity steam for self cleaning, proper mixing and no need for costly external modulation or control valves. Our K and M series models feature a manual or automatically adjustable combining tube to shear, ribbonize and control the slurry and ensure complete cooking of the process fluid. This eliminates hammering, noise and ensures a complete and consistent cooking process.
Patented internal modulation DSI unit

15. Contrast: Sparging vs. DSI
Paper mill – actual data
Reduced steam usage by 33%
932 lbs (422 Kg) with spargers
624 lbs (283 Kg) with DSI
Time Savings
Daily production increased by 32%

16. Maximum Boiler Energy Efficiency
100% efficient use of steam heat energy
Reduced steam consumption
Less energy required at boiler
25% - 30% reduction is common
Lower energy costs
Direct Steam Injection heating technology is extremely energy efficient and can represent a significant part of a business’ energy reduction and sustainability initiatives. DSI systems transfer 100% of steam’s sensible and latent energy to the fluid to be heated. This reduces the amount of steam necessary which in turn lowers the energy requirement at the boiler. In fact, when comparing to a shell & tube or plate & frame style heat exchanger, DSI systems are typically 25-30% more efficient. With energy costs unstable at best and continuing to rise, many of our customers are realizing annual savings in the hundreds of thousands.
rev 3.09

17. Energy Comparison Report
Process fluid to be heated
Process flow rate
Incoming temperature
Desired temperature at output
Available steam pressure
% of condensate returned to the boiler
Boiler makeup water temperature
Hours per day in use
Boiler fuel cost per million Btu
If you are using heat exchangers and would like to know how much a DSI system can reduce your energy costs, please gather as much information as you can about your specific operating parameters and check with a direct steam injection engineer.

18. ENERGY Calculator Process fluid type In/out temperature
Process flow rate
Hours per day in use
Steam pressure
% condensate returned
Boiler makeup water temperature
Boiler fuel cost per million BTU
Energy.gov

19. Precise Temperature Control = Efficiency
Poor Temp Control
Tight Temp Control
Tight temperature control results in Lower set-point
Beyond the achievable energy savings demonstrated in the ROI calculator, there are additional, inherent advantages of using direct steam injection compared to a heat exchanger.
A heat exchanger is slow to respond to varying conditions (steam pressure, incoming water temperature) causing a wide variation in discharge water temperature. Because of this inefficiency, in order to achieve minimum set points with a heat exchanger the target set point is set higher compared to a DSI heater which accurately controls temperature and adjusts immediately to varying conditions.
In addition, because of the direct steam heating efficiency, the required set point is lowered, resulting in overall less steam usage (reducing carbon emissions by using less natural gas to make steam).

20. Direct Steam Advantages
Reduced steam consumption
Significantly lower energy costs
Low maintenance
Handles fluids that are difficult to heat—avoids “burn-on”; highly viscous or abrasive slurries are no problem
Small size
Consistent, precise discharge temperature
No condensate return required
Direct Steam Injection technology offers significant advantages over less efficient indirect methods of heating process fluids. Whenever it is determined that some slight dilution is acceptable, this technology should be considered.

21. Sustainability & the Triple Bottom Line
Sustainability Triangle
Economic
Sales, profits, ROI
Jobs created
Taxes paid
Environmental
Air, water quality
Energy usage
Waste produced
Social
Community impacts
Product responsibility
Firms that maximize the sweet spot thrive in changing environments

22. Direct Steam Injection Technology Real-World Results Case Studies

23. Typical Food Processing Applications
Utility Heating
CIP and COP water heating
Washdown hose stations
Jacketed kettles
Sterilization pots
Can topping
Bottle and can rinsing
Thermal inactivation
Process Heating
Pet food processing
Thick stock/paste heating
Baby food/formula cooking/pasteurizing
Sauce heating/thickening
Soup base cooking
Condiments heating
UHT pasteurization
Starch cooking
SPEND TIME ON THIS SLIDE Explain some of these in more details ~ give examples
Meat and poultry sanitizing importance ~ 180F USDA regulations
Cleaning/sanitizing lines at major soda and beer mfg
Can topping at major veggie canning plants ~ replacing HX’s
Jacketed Kettles to eliminate hot spots and burn on in dairies for example
Sanitary DSI heaters are used in a variety of applications where FDA or USDA requirements need to be met. 23

24. Success #1 Processor Reduces Cycle Time (Slurry Heating)
Meat slurry cooking
Customer needs to give permission to use name, or use a ‘not to be named’ company format

25. Success #2 Plant Improves Throughput (Water Heating)
Jacketed vessel tanks
Replaced inefficient tank sparger
Scaling clogged heater
Steam hammer damaged tanks
DSI benefit impact
Self-cleaning design increased uptime by 20%
$2000/month saved by eliminating tank welding repairs
Consistent temperature set-point maintained
60°F incoming water raised to 200°F
400 gallons per minute (widely fluctuating)

26. Success #3 Firm Improves Product – Slurry Viscosity
Product in extruder - viscosity kept at acceptable levels to run smoothly and faster
Save time
Save energy

27. Summary: DSI = Sustained Benefits
DSI effectively transforms heat energy
Near-instantaneous energy (heat) transfer
Effectively 100% efficient
Significant measurable sustainable benefits
Energy savings
Sanitation effectiveness
Lower production costs
Reduced maintenance costs
Productivity improvement
More work gets done = more bottom line profits!
Simply ~ We transform Energy, HX’s transports it!

28. David Degelau Hydro-Thermal Corp 262.548.8900 400 Pilot Court
Engineer, Certified Steam System Specialist
400 Pilot Court
Waukesha, WI