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Direct Steam Injection Heating for the Wastewater Industry

Maintaining consistent sludge temperature in the Municipal, Agricultural, or Industrial markets can be challenging. If you are looking for a more efficient, cost-effective solution for heating your sludge without the scalding that can occur with a heat exchanger, then Hydro-Thermal has your solution.

Realize major cost savings with precise temperature control to aid in the anaerobic digestion process by keeping microorganisms at the required temperature to optimize effectiveness and increase methane gas production to power the boilers.

Hydro-Thermal’s patented designs can handle highly viscous slurries without burn on, plugging, or fouling typically resulting from other technologies, achieving thousands of dollars in energy savings.  

Hydro-Thermal's patented DSI heating system works by mixing steam and process liquids completely while delivering consistent temperature and instantaneous heating. For more information on our advanced direct steam injection technology, click here

Applications for Municipal, Agricultural, and Industrial Wastewater

Anaerobic digester sludge heating – recirculation or preheating

A reliable heating source for anaerobic digestion is imperative to ensure production (or capture) of biogas/methane.

What does your plant need from an Anaerobic Digestion Heater?

Heating Flexibility

A DSI heater can replace or augment a heat exchanger depending on boiler capacity. Achieving precise temperature control for increased biogas generation is challenging, especially in the winter months.

Precise temperatures without fear of scalding

Achieve ideal temperatures of 85-100°F (29-38°C) for mesophilic digestion or 120-140°F (49-60°C) for thermophilic digestion to optimize biogas generation. Direct steam injection provides a gentler form of heating that will not scald or kill bugs. 

Non-Obstructing Heater (NOH) design that reduces maintenance 

The NOH's design can ensure that rags do not get caught in the heater. The NOH can be produced using non-corrosive metallurgies that can withstand grit and highly abrasive materials.

Space Savings 

The NOH is a fraction of a heat exchanger's size, freeing up valuable plant space.

Hydro-Thermal Anaerobic Digestion Heater Solutions


Combined with HTC’s NOH design and the process inputs given for the application, Hydro-Thermal has the optimal solution.

Digester Heating - Reclaimed heat with a pump

Digester Preheating

Digester Recirculation Heating

Click here to learn more by reading our industrial wastewater case study 

Click below to watch a short informative video on the NOH heater

Industrial Pretreatment

Heating during industrial pretreatment is imperative to optimize separation, leading to an increase in oil yield. 

What does your plant need from a Pretreatment Heater? 

Maximize fats, oils, and grease (FOG) extraction while reducing or eliminating breaker chemicals

Hydro-Thermal's non-shear heater will heat the FOG waste stream to the optimal temperature to maximize oil extraction via a centrifuge, decanter, or tricanter process. With precise temperature control, oil yield (and ultimately revenue) can be increased. 

Optimizing oil extraction is governed by Stoke's Law. Several factors make up Stoke's Law. Using Hydro-Thermal's non-shear heater help decrease the viscosity and increase the relative density of the waste oil stream, resulting in increased yield. The added temperature enables a possible reduction in emulsion breaker chemical dosing.

Tank Heating

Easily and efficiently heats tanks on in-feed or in recirc mode (trim heat). We can heat the fluid going into the tank, re-circulate the tank to maintain a specific temperature, or leave the tank cold and heat the liquid exiting the tank, producing hot water on demand.

  • Click here to learn why tank heating is more efficient by utilizing a Hydroheater vs. a sparger.

PDF Resources

      Industrial Pretreatment              Heating Digester Slurries              Anaerobic Digestion                     Wastewater Whitepaper                                       

   Industrial Pretreatment                         Heating Digester slurries                              Anaerobic digestion                       Wastewater whitepaper                     



Learn More...

For more information on our products, click here.

For more information on our patented direct steam injection technology, click here.

Looking for a quote? Fill out this form.

How Does Direct Steam Injection (DSI) Work?

Direct steam injection works by directly injecting steam into a process fluid to obtain more rapid heat transferring, resulting in more efficient energy usage than indirect heat exchangers. This efficient process of heating is caused by our direct steam injection Hydroheaters’ ability to control both steam flow and mixing turbulence by using a modulating stem plug and nozzle or diffuser assembly in the heater. This precise mixing of a measured amount of high-velocity steam directly with your liquid or slurry provides an instantaneous transfer of heat from steam to the liquid. This method of heat transfer allows for 100% thermal efficiency and energy savings of 20-25%. Don’t believe us? Head over to our Energy Savings Calculator to get an accurate estimate of how much you can be saving in operating costs.

To accomplish this, a precisely engineered, variable-area steam nozzle or diffuser meters the flow at the point of injection and contact with the fluid. The large pressure drop from full steam pressure to the process fluid pressure ensures high-velocity choked steam flow and instantaneous mixing of the two streams. When steam flow is choked, its velocity at the nozzle or diffuser exit is constant regardless of the total mass flow injected. The internally modulated Hydro-Thermal heaters control the amount of injection area (cross-sectional area of the nozzle or diffuser opening) to precisely regulate the heat load. The constant steam velocity results in consistent and stable operation across the full range of operations.

Hydro-Thermal’s patented direct steam injection heaters use direct heat exchange as a means to transfer 100% of the steam’s energy for heating liquids and slurries over a wide range of viscosities and solid contents to precise temperatures. A Hydroheater’s internal modulation assures exacting steam control, rapid temperature management and produces predictable results. Each Hydro-Thermal heater has an internal trim custom designed for each customer’s specific needs and requirements.

How Direct Steam Injection Works - Hydroheater

DSI Technology

Hydroheaters/Jetcookers commonly outperform other forms of direct steam injection and indirect heating methods such as heat exchangers. Use the links below to learn more about how Hydro-Thermal’s patented technology outperforms the status quo.

  • External Modulation vs Internal Modulation Button
  • Direct Heating vs Indirect Heating Button
  • Types of Direct Steam Injection Button

External vs. Internal Modulation:

Externally or Internally modulated direct steam injection refers to how the mass flow of steam injected into the process fluid is controlled.

External modulation uses a steam control valve on the supply line to vary the pressure of the steam at the point of injection: Varying the pressure changes the steam density and velocity through the nozzle to control the amount of heating. Regulating steam pressure to control heating can result in unstable operation, hammering, and vibration when high or low steam flowrates are required. At low steam flow, i.e., trim heating, the differential between steam pressure and the process can be very small, and a slight fluctuation in either pressure can cause an upset. Alternatively, at high steam flow requirements, i.e., max heating at startup, the orifice or nozzle size will allow more steam than can be condensed, and steam hammer occurs.

Internally modulated DSI controls the injection area rather than steam velocity and density to regulate the amount of heating. An internally modulated heater operates at higher steam velocities compared to external modulation. This higher velocity produces improved, often rapid mixing and nearly instantaneous condensation of the steam into the process fluid.

External Modulation
Internal Modulation

External Modulation

Internal Modulation

Direct vs. Indirect Heating:

There are two basic types of heat exchangers used to transfer heat between process fluids — direct heat exchange and indirect. Indirect heating is most commonly seen in the form of plate & frame or shell & tube heat exchangers. Any process that does not allow direct mixing of steam and fluid is indirect heating. Heat exchangers transfer heat through a membrane or solid wall. This results in only ~ 83% of the heat energy transferred to the process fluid. In contrast, the remaining energy is discharged in the condensate formed from the steam.

On the other hand, direct heating uses 100% of the steam’s heat energy by adding steam directly to the process fluid.

The benefits of using direct contact heating vs. indirect include:
  • Energy savings of 25% or more
  • Precise and instantaneous temperature control is possible to within 1°F
  • Reduced footprint for direct steam injection system
  • Reduces maintenance via self-cleaning and elimination of a condensate return system
Additional benefits:
  • Rapid and uniform heating -important in starches and food product
  • Can heat highly viscous fluid
  • Handles fluids that are difficult  to heat—avoids “bake-on”; abrasive slurries
  • Eliminates plugging and fouling of the heat transfer surface
  • Rapid response time
Indirect Heating
Direct Heating

Indirect Heating

Direct Heating

Types of Direct Steam Injection (DSI)

Hydro-Thermal’s heaters utilize direct steam injection. This general term refers to any type of fluid heating that uses steam being directly mixed with water or process fluid. There are many forms of direct steam injection, including spargers, eductor pumps, externally modulated heaters, and internally modulated heaters. Each method varies in its levels of complexity, with sparging being the most simple and internally modulated, having the greatest level of technology and control.

Internal Modulation

Hydro-Thermal’s technology, which utilizes internal modulation, is the most advanced form of direct steam injection. It has many benefits over other direct heating methods, including:

  • Reduced steam consumption
  • Significantly lower energy costs, 100% efficient use of steam energy
  • Low maintenance
  • Handles fluids that are difficult to heat—avoids “burn-on”; highly viscous or abrasive slurries are no problem
  • Small footprint
  • Consistent, precise discharge temperature
  • No condensate return required
Direct Steam Injection - How it Works


Sparging is the oldest, most straightforward and least complicated technique for mixing steam with liquid or slurry to affect heating. It is injecting steam directly into a fluid-filled tank. Though considered inexpensive and straightforward, sparging is very inefficient, and the operation invariably results in:

  • Poor heat injection economics due to steam energy escaping from vessels without condensing.
  • High maintenance costs for tanks, sensors, and piping are the norm if the equipment operates outside the design parameters.
  • 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 direct steam injection heating method.
  • Non-uniform heating

Sparge Tube

The externally modulating 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. Still, they 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.

Additionally, if low (trim heating) or high steam flow is required, the spring mechanism can have difficulty with accurate or stable control. Spring failure is a common issue with this type of heater. Additional drawbacks of sparge tubes are:

  • 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 wear and breakage
Sparge Tube

Mixing Ts

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 is not the best choice for process fluids. When used for water, mixing tees are prone to scaling, fouling, and excessive hammer. Their operation often requires steam and water pressure to be very close to each other for balanced mixing. When either steam or water pressure fluctuates slightly, the higher pressure line can overcome the other and backfill the piping. This can result in live steam discharging the system. The drawback of Mixing Ts are:

  • Very high maintenance
  • Prone to scaling and fouling
  • Steam hammer is common
  • Potentially very dangerous due to live steam being close to human contact
  • Limited temperature control
Mixing T's

Want to learn more:

  • Benefits of direct steam injection button
  • Get a quote button
  • Contact Hydro-Thermal button
  • PDF Downloads - direct steam injection technology button
  • Videos button
  • Case Studies Button


Hydro-Thermal’s Response & Strategy for Covid-19

As an essential company, we are open for business and fully operational during these unprecedented times.

Our hours of operation will remain the same - Monday – Friday 7:30 a.m. – 4:30 p.m. (US Central Time). Feel free to call us at (800) 952-0121 or contact us with any questions or concerns. 


Travel to Customer’s Sites

Our heaters and skids are often used in critical applications in our customer’s facilities. Because of this, it is of utmost importance that our Service Technicians get the chance to service our heaters and skids so that our customer’s stay up and running.

With wide ranging rules for who can visit our customers’ sites, below are some options that should help determine how we can best serve you.

  • Service Tech site visit – provide preventive maintenance, training of your staff, identify need for critical spare parts to stock, etc.
  • Industry/Application Experts site visit – evaluate potential applications that would benefit by having our heater or skid there and show the benefits to you (increased production and reduced energy usage, for instance).
  • To minimize visits, have both the Industry/Application Experts and the Service Techs visit together. With this you get, 
    • Heater maintenance
    • Staff training
    • Identify areas where we can help improve processes, energy usage, other efficiencies, etc.
  • If virtual meetings work best for you right now, we work daily with MS Teams, Skype, Zoom, GoToMeeting, etc. so we are happy to meet you in the virtual world, too.


Visitor Policy

In order to protect our employees and business visitors during the pandemic, Hydro-Thermal has implemented the following guidelines for visitors:

Hydro-Thermal is allowing visitors on a very limited basis under the following guidelines:

  • Only scheduled business visitors with specific topics to discuss are welcome.
  • There must be at least 24 hours of advanced notice prior to the visit. Visiting groups should be limited to two (2) representatives.
  • Visits should start and end on time and be limited to a defined area. 
  • Visitors must wear masks
  • Visitors will be asked to fill out and sign a short health survey when they arrive:  
    • Have you come into contact with someone who has been diagnosed with Covid-19 within the past 14 days?
    • Have you had any of the following in the past 72 hours:  fever, chills, shortness of breath, difficulty breathing, body aches, headache, loss of taste or smell or sore throat?  


What is Steam Hammer & How to Eliminate Steam Hammer

Steam Hammer/Cavitation/Vibration

If your heating equipment is violently shaking, then it is a concern that needs to be addressed. It is not only dangerous, but it also can be an expensive maintenance problem. Externally modulated technologies such as heat exchangers or unsophisticated forms of direct steam injection, such as spargers, can cause steam hammer.  For more information on external vs. internal modulation, direct and indirect heating, and the spectrum of direct steam injection products, click here.


Why is Steam Hammer Happening?

There are multiple reasons why this cavitation issue could be occurring. Below are a few common scenarios.

  • Uncondensed steam causes bubbles to form and collapse on tank walls, causing hammer and damage to the tank and peripheral piping.
  • Check if you have an externally modulated steam pressure valve. This type of operation can lead to steam hammer or unit vibration as the steam mixes with the process fluid in the piping or tank. Over time, this can contribute to equipment wear, piping damage and lead to poor performance. If you have an externally modulated valve, consider purchasing an internally modulated option, which eliminates the problems associated with hammer and vibration. 
  • Monitor flow changes. Ideally, they should be gradual, and the temperature control loop should be able to respond to these changes. Review the initial sizing conditions provided to the equipment manufacturer. If production has increased or processing conditions have changed, the equipment may no longer be properly sized. Updated equipment or new components may be needed to compensate for these variations.
  • Check your steam line for condensate. If there is excessive condensate in the steam line, then hammering and vibration could occur. If needed, purge the steam line. Depending on the piece of equipment, a drip leg and condensate trap may be recommended. Check with the equipment manufacturer for their specific recommendations. 

Why is Cavitation a Concern?

  • Inconsistent steam mixing and heat transfer leads to product inconsistency and wasted energy.
  • Imprecise temperature control from steam hammering translates to higher energy costs.
  • Tanks walls can be damaged, leading to maintenance headaches from welding over the damaged sections of the tank. Damaged tank walls can also be a major safety concern if hot water and hot steam would shoot out of the sides of a tank.
  • Steam hammer can lead to a process equipment failure if the problem is severe enough. Not to be mistaken for water hammer that occurs in piping systems that utilize quick closing valves or that do not have a proper attenuation system, steam hammer is a result of uncondensed steam instantaneously cavitating on the tank wall or piping with damaging force.


How can you Prevent Equipment Vibration?

Steam Hammer

Hydro-Thermal’s patented direct steam injection heaters and skid systems are designed to eliminate steam hammer and vibration, among other benefits. Hydro-Thermal’s internally modulated Jetcooker™ utilizes a single nozzle which focuses the incoming steam and accelerates it to a very high velocity (usually sonic velocity) before it comes into contact with the process fluid. This high velocity helps to atomize the steam bubbles and shear the incoming process fluid, which allows for a more complete, efficient heat transfer. The result is no steam hammer, precise/uniform heating, and reduced maintenance. 

Contact us today to get a free evaluation from our application experts. They can provide tips on how to optimize your heating and eliminate steam hammer.  

Not only will a Jetcooker™ help eliminate steam hammer and equipment vibrations, but it will also improve your process efficiency. Receive two benefits in one by replacing your current heating system for one that can improve ROI. Head over to our Steam Energy Saving Calculator to discover how much you can save along with eliminating steam hammer.


Our Internship Program at Hydro-Thermal

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Sanitary Hydroheater (Product Video)

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EZ Heater (Product Video)

Infuze Heater (Product Video)

Your Internship at Hydro-Thermal - 2018

Your Internship at Hydro-Thermal - 2017

What is Direct Steam Injection?

Hydro-Thermal ~ Competitive Advantage

Hydro-Thermal Talks Direct Steam Injection

Hydro-Thermal - Celebrating 80 years of Steam Innovation

Hydro Thermal - Scott Walker

Hydro Thermal's Passionate Employees

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Hydro-Thermal is the global leader in the development and manufacturing of Hydroheaters. Through our vast global channel partners, we support hydro heating in six continents and all industrialized areas. We create heating systems for a variety of industries including: pulp, paper, chemical, ethanol, food & beverage, metal, & more!

Hydro-Thermal Corporate 

400 Pilot Court
Waukesha, WI 53188 USA
Phone: (262) 548-8900
Fax: (262) 548- 8908