High-Pressure Steam Generators


The high-pressure steam generator produces non-toxic process heat.

NUK® High-Pressure Steam Generator

The NUK® High-Pressure Steam Generator is a closed-looped (hermetically sealed) system that produces steam for high-temperature applications. Therefore, this steam generator is able to produce non-toxic process heat while offering the same advantages of a conventional hot oil system.

Oil Deodorization

Sigma Thermal developed the NUK ® specifically for the application of oil deodorization, typically used within the food industry. During deodorization, the NUK is used as a heat source in the process to safely remove undesirable flavors and odors from edible oils; leaving the oil free from toxins.

Submit an RFQ – To specify your high-pressure steam generator.

This hermetically closed-looped system consists primarily of a vertical cylindrical combustion chamber, coil, burner and supply and return manifolds.

Chamber walls are lined with vertical pipes with continuously-welded longitudinal fins. The pipes are connected to a lower manifold (fed with condensate) and upper manifold (connected to the steam outlet). Often designed to section VIII Division 1, the heater remains flooded with fluid through the systems level control. This eliminates the need for boiler operation.


  • Low NOx Emissions (w/optional equipment)
  • High efficiency
  • Non-Toxic Heat Media
  • Fuel Versatility
  • Natural Circulation (No Pumps)
  • No feed water system
  • Minimal Maintenance
  • Designed & Built to ASME code

Transfer Media


Design Features

  • 0.5 - 15 MM Btu/Hr
  • Atmospheric – 1950 PSI
Flow Rate
  • 824 – 24,790 lb/hr.
  • 80% LHV (typical)
  • 90% or better with Combustion Air Preheater
Burner Turndown
  • 10:1 (standard)
  • Natural Gas
  • Propane
  • Fuel oil #2- #6
  • Digester gas
  • Dual fuel
Burner Configuration
  • Top mounted burner fires downward. Flue gases are forced through a three-pass system, heating the water in the tubes. Steam generates naturally and is conveyed (without pumps, etc.) to the deodorizer. As the steam loses its heat to the deodorizer, it condenses and flows back to the NUK and the cycle repeats.
  • The NUK® riser tube arrangement consists of annulus-shaped headers and multiple vertical risers. The vertical riser tubes provide a cylindrical heating surface. This vertical riser tube design eliminates the possibility of vapor lock during load functions.
Coil Design
  • Includes two coil baskets (one nested in the other), consisting of ring type headers and connected by vertical risers.
Low NOx Options
  • With optional equipment we can achieve typical application ranges of 30-60ppm NOx. Ultra Low NOx systems (5ppm) are available to meet the most stringent emissions requirements including California SCAQMD (South Coast Air Quality Management District).

"Open" vs. "Closed-Looped" Design

There are many reasons why the NUK “closed-looped” design is more beneficial than the conventional “open” boiler design.

Conventional “Open” Boiler Design
  • Possible traces of toxic fluids found in edible oils
  • Less Efficient: 15-20% heat capacity lost through flash/ blowdown.
  • Complex and costly feedwater treatment system required.
  • Circulation pumps required
  • Corrosion possible
  • Vapor locking possible due to fluctuating heat loads
NUK® “Closed-Looped“ Design
  • Edible Oils remain clean
  • More Efficient: Flash/blowdown doesn’t occur.
  • Feedwater system not needed
  • Circulation pumps not needed.
  • Corrosion avoided due to pressure and vacuum-- tight construction
  • Eliminates vapor locking

Control Panel

All systems include burner management systems, single loop controllers, and limit controllers to comply with NFPA requirements. The control system is designed to provide a pre-purge and post-purge of the heater, automatic ignition, low flame start (high turn down burner), continuous main flame detected by UV sensor.

Control options are virtually limitless with relay logic and programmable logic systems available. User interfaces can be as simple as indicators and push buttons or as advanced as PC-based controls.

Standard relay logic based control panels are used on all equipment to provide a cost effective control system. They are relatively simple and reliable and provide adequate communication to the customers’ control systems (DCS).

Auxiliary Equipment

Sigma Thermal Heaters are available with any of the following auxiliary equipment can be provided separately or designed into an integral skid, size and transportation requirements permitting.

  • Economizers
  • Combustion Air Preheaters


Sigma Thermal Energy packaged systems are skid mounted, wired, and assembled to the maximum possible extent before shipment to reduce installation time and labor. Packaged systems undergo a Functional Acceptance Test (FAT) which tests the proper operation of the burner management system, controls, instrumentation, and valves. This ensures that a Sigma Thermal Energy system will be ready for a quick and easy start up as soon as it arrives to the job site.