Industries
Introduction to Quicksteam boilerEconomic Justification

Heat Recovery Steam Generators

A petrochemical plant may have production units that generate heat. These plants usually have a steam generator (heat recovery boiler) that converts the heat production to steam. This additional steam production allows the powerhouse to burn less fuel thereby reducing the plant’s need for fossil-fuel energy. However, upon an emergency shutdown of the heat-generating unit, the steaming rate out of the heat recovery boiler will drop to zero and the boilers will need to increase their steaming rate by an amount equal to the steaming rate of the recovery boiler in order to keep the steam pressure constant. To do this, enough boilers have to be in backup mode to be capable of matching the steaming rate of the recovery boiler.

Operating Conditions

  • Recovery Boiler Production: 120,000 pph
  • Boiler A: 20,000 pph (20% of 100,000 pph MCR)
  • Boiler B: 20,000 pph (20% of 100,000 pph MCR)
  • Vented Steam: up to 40,000 pph (2,880,000 $/year)

Cogeneration

Steam produced through cogeneration is typically cheaper than steam produced using a standard boiler. Since the difference in the price of steam is generally due to the additional power being generated, maximizing the production of cogenerated steam increases the power production and reduces fossil-fuel consumption. When an emergency shutdown of the cogeneration unit occurs, its steaming rate drops to zero and the backup boilers need to increase their steaming rate by an amount equal to the steaming rate of the cogeneration unit in order to keep the steam pressure constant. This can only be done if enough boilers are in hot backup mode prior to the cogeneration trip.

For a cogeneration facility this means that:

  • Boilers in backup mode constantly “rob” megawatts away from the steam turbine in order to fulfill their role as backup steam generators which increases operating costs
  • Enough boilers need to be in backup firing mode to ensure that no trip occurs during an increase in the firing rate. (more boilers = increase in capital cost).

As shown in Figure A, the Enero QuickSteam boiler combines two technologies:

  • An energy storage vessel that consists of a pressurized saturated water-steam vessel. The purpose of the steam accumulator is to keep a large amount of saturated water at a pressure above the steam header pressure. If one or more boilers were to trip, the accumulator would start dropping its internal pressure. The drop in pressure would, just like a pressure cooker, force part of the water inside the accumulator to flash into steam. Steam accumulation is not well known in the industry because it can only steam for a limited amount of time (limited amount of steam stored). The total steaming capacity of the steam accumulator is a function of:
    • The main steam header (the lower the pressure, the more a potential amount of steam can be vented)
    • The accumulator pressure (the higher the internal pressure, the higher the stored energy and the higher the accumulated steam)
    • The amount of stored saturated water (the more water there is in the accumulator, the more the amount of accumulated steam)
  • A series of compact steam generators (in this case a coil boiler) can change the load very quickly without damaging the boiler’s internals. The coil boiler is a small and compact steaming unit that relies on a water coil that minimizes the stress involved in the warm-up phase of boiling. For example, a coil boiler will take 5 minutes to go from cold to full maximum steaming rate while a standard water-tube boiler could take a minimum of 20 minutes to do this. Coil Boilers are seldom seen in manufacturing and are almost always seen in institutions such as hospitals. Some of the reasons Coil Boilers are not used in industry include:
    • Coil Boilers are small (MCR up to 20,000 pph) and it is not economical to use these type of boilers for steam demand higher than 60,000 pph.


Description of the Enero QuickSteam Boiler

The Enero QuickSteam Boiler is a new type of high-efficiency boiler that can reach its full steaming capacity in 30 seconds from a cold start and is thus capable to respond to rapid, large and unpredictable changes in steam load.  The rapid speed of response from the Enero QuickSteam Boiler provides additional flexibility to steam system operation and design allowing plants to reduce their energy costs.

The Enero QuickSteam Boiler uses fossil-fuel as its energy input and is the ideal solution for cogeneration plants or heat recovery generators. For these types of applications where steam backup is essential, the Enero QuickSteam Boiler is a more robust solution that keeps fuel consumption down to almost zero during no-load operations.   

Characteristics of the Enero QuickSteam Boiler:

  • The Enero QuickSteam boiler is designed with heat storage capability enabling it to reach its maximum steaming capacity (MCR) from a cold start in less than 30 seconds
  • Once reaching its MCR, the Enero QuickSteam Boiler can:
    • Ramp its steam production rate back to zero and shut the burners off (Peaking demand control)
    • Modulate the firing rate, revert to cascade control and control the steam plant pressure through the Plant Master Controller (Backup generation control)
    • Minimize steam pressure excursions during large load disturbances (Transient demand control)
  • The Enero QuickSteam boiler reacts quickly to steam load disturbances minimizing steam header pressure variations

 

 

 

Figure A: Schematic of the Enero QuickSteam Boiler