HRC – Thermo Acoustic  “Harmonic Resonance Combustion Technology”

 

Thermo-acoustic high frequency pulse detonation technology a HRC or Harmonic Resonance Combustion System is superior the conventional steady state burner and combustion systems commonly used in the heat transfer and boiler industry. Superior, not only in terms of energy efficiency but also in the reduction of greenhouse gas emissions.

This pulse detonation is a new technology which uses sound and high frequency shock pressure waves to drive and sustain a pulsating and turbulent combustion process that facilitate instant heat and energy exchange from fuel to useful process heat.

This pulse detonation process is a more efficient and complete than can be achieved with conventional burner systems, the efficiency and completeness of the process is due to its turbulent combustion environment and internal shock pressures in waves of the detonation cycles, resulting in extremely high heat and mass transfers with reduced greenhouse gas emissions.

Intellectual Property Protection

Currently the Delafield Patent Pty Ltd has patents in several counties and all its IP is protected by intellectual property right and trade secrets to cover;

Pulse Detonation process and method

The design and configuration of the detonation chambers.

Use of pulse detonation in conjunction with the chamber designs and orientation.

Use of detonation technology in production of hot water, steam, dry heat  for all and any use in hot water and steam provision, food industry, sterilisation of foodstuffs and other materials by heat using pulse combustion to detonation.

 

A new generation combustion technology

Technology Explained

HRC  Harmonic Resonance Combustion

High Fuel Efficiency & Ultra Low NOx Emissions combustion system

 

Delafield’s solution to the problems and shortfalls of existing conventional burners and pulse combustion technologies is Harmonic Resonance Combustion HRC the result of a totally new approach to the basic combustion process and what happens to the various chemical processes, components and gases.

We understand that with conventional burners the fuel burns with oxygen to its most stable oxidised state, the energy released is called the heat, this heat is extremely useful for commercial and industrial purposes but this needed to be achieved in an efficient and environmentally responsible manner.

Many fuels contain elements other than carbon, and these elements may be transformed during combustion. Therefore, combustion is not always complete, and the effluent gases may contain NO, NO2 and unburned or partially burned products in addition to CO2 and H20.

What is HRC?

HRC is a new technology that uses a combination of sound pressure waves and the momentum of a gaseous mass to repeat and sustain an intermittent detonation process. This device uses an explosive process where heat energy is released in a cyclic turbulent environment and the fuel molecules are almost instantly oxidised into CO2 and H2O with minimal by products and formation of NO and NO2.

HRC or Harmonic Resonance Combustion, high frequency pulse detonation, is the consequence of a combustion instability that is driven into resonance by the geometry of the combustion chamber. Normally combustion engineers avoid combustion-generated instabilities at all costs, since they can very quickly lead to catastrophes. Here we actively utilise the instability to gain a number of advantages. This resonant driving locks the combustion instability into a very stable repetitive pattern at the resonant frequency, which can be anywhere between 1Hz to 20,000Hz, but more frequently lies in 1,000Hz and 8,000Hz range. The detonation process becomes self-aspirating and without the need to continuously force a supply of combustion air to overcome the acoustic pressure waves. The flame is not continuous but a series of discrete flamelets that are ignited by the hot remnant gases of prior cycles. Here we actively utilise the combustion instability to gain a number of advantages.

Overall heat transfer and mass transfer coefficients are two orders of magnitude higher than conventional systems. The implications of this are that the size of the equipment can be reduced, i.e. the heat transfer area can be more than halved to carry out the same duty as a forced convection conventional combustion system, supplying heat to processes.

The acoustic pressure waves cause the gases (fuel, air and combustion products) and material in the combustion chamber and exhaust to oscillate rapidly. This has at least three known effects that cause an increase in the transfer rates:

  • The heat boundary layer never gets a chance to establish itself and consequently it is always trying to develop.
  • The temperature and concentration gradients at right angles to the mean flow are periodically extremely large.
  • The heat transfer surfaces experience micro-vibrations that increase the heat transfer.

These effects are more than cumulative and as a result the heat transfer coefficients are at least two orders of magnitude greater than in conventional systems. We have seen evidence of a fourth effect increasing the heat transfer rate in which there is a thermal pressure wave travelling into the material being heated. This has also been theoretically postulated by Merkin & Pop, whose theoretical work indicates that there should be thermal pressure waves assisting the heat transfer into the bulk of the material being heated.

Why use HRC pulse detonation?

Because it completely burns fuel and reduce emissions, this results from the following aspects;

  • Reduced flame temperature and more turbulent combustion environment.
  • Low levels of excess air.
  • Highly repetitive, intermittent HRC
  • Acoustic flow field causes,( in this case propane C3H8) molecular fuel oxidation where bonds are broken and bond are made to form simpler constituent parts such as CO2 and H2

Propane undergoes combustion reactions in the presence of oxygen, when propane burns completely it will to form water and carbon dioxide.

Propane + oxygen → carbon dioxide + water

C3H8 + 5 O2   →   3 CO2 + 4 H2O + heat

Some other beneficial effects of a complete combustion process in a turbulent and high frequency intermittent and cyclical environment are:

  • Overall heat transfer and mass transfer coefficients that are two orders of magnitude greater than conventional systems. The implications of this are that the size of the equipment can be reduced for industrial process.
  • Exhaust gas emissions from pulse combustion and detonation are amongst the lowest available in the world, NOx levels about a quarter of those proposed for the latest Californian emissions. Most people are only worried about the nitrogen dioxide (NO2) emissions, but they should also be concerned about the nitric oxide (NO) emissions as they can rapidly turn into NO2. Pulse detonation systems can deliver NOX emission levels (i.e. NO plus NO2) as low as 1 to 3ng/J of useful heat. Current mandated levels of total NOX are at the 40ng/J of useful heat level. The proposed levels for California are 9ng/J of useful heat. Raising the inlet air temperature of the ‘HRC”, to conserve energy, does not increase the NOx levels, as would normally be expected with conventional systems.
  • Total hydrocarbon (THC) and carbon monoxide (CO) levels of zero. In the best of conventional combustion systems there are usually small quantities of unburnt hydrocarbons and CO present in the exhaust gases.
  • Thermal efficiency of systems can be as high as 94%. This includes parasitic energy, which in the case of pulse detonation is minimal and only occurs at start-up. For other combustion systems, forced convection, via fans, is used to increase the efficiency, but these can consume about 3% of the energy supplies.
  • Emissions per unit of energy are dramatically reduced.

There are many processes that can have their thermal input supplied by pulse detonation.

Pulse Amplitude

NOx reductions as a function of the pulse detonation amplitude

The above figure shows what happens to the NOX in a flame as the amplitude of the pulsing is increased. This causes two things to happen:

  • The flame gets stretched. As a consequence fuel fragments or radicals are no longer produced or their concentration is greatly reduced that their contributions to NOX production chemistry is almost eliminated.
  • The resulting acoustic flow field also causes local exhaust gas recirculation. This suppresses NOX formation by making it much harder for more NOX to be produced.

It is because these two effects are occurring in pulse detonation, that it is possible to preheat the incoming combustion air without causing the NOX levels to substantially increase.

 

How does HRC actual work and its effect on heat transfer?

This Patented Thermo-acoustic device consists of multiple interconnected chambers and cavities to achieve the desired thermal output. The main sections that make-up this system are; Fuel intake plenum, intake duct, detonation chamber, resonance chamber and decoupling chamber. (fig.1)

Flow Diagram

This detonation device uses pressure waves and the mass of the gases, present in the intake duct and resonance chamber of the device, as its virtual piston to drive the detonation cycle; instead of a mechanical reed or flapper valve as commonly used in other pulse combustion devices.

For flow and wave diagrams Fig.1 to Fig.6 see the following HRC diagram.

HRC Diagram

 

The detonation cycle start (fig.2) when the detonation chamber is loaded with fuel and the fuel is ignited by a spark or flame; the fuel detonation creates a large amplitude pressure wave that drives the surrounding gases away from the detonation chamber. (fig.3)   This volume of gases, at the inlet side in the intake duct, and on the outlet side in the resonance chamber, have significant mass, because of this, the mass, it is not driven away instantly by the detonation pressure wave but is accelerated over a fraction of the

cycle time. In this detonation device, the gas mass in the intake duct is a small fraction of the gas mass in the resonance chamber; this is due to different geometry of the intake duct and resonance chambers. This means that the intake duct air mass will be driven away from the detonation chamber much faster than the larger mass in the resonance chamber. (fig.4)  The synchronisation of the carefully designed imbalance, of these two gas masses, is critical for the frequency and timing of the detonation cycle.

When the detonation is initiated by ignition of fuel in the detonation chamber, a wave of significant high pressure propagate outwards from the detonation chamber, through both gas masses acting as a compression wave. (fig. 4) This wave moves through both the intake duct and resonance chamber gas masses and travels with high velocity, greater than the speed of sound. The gas mass in the resonance chamber is significantly increased in temperature as a result of the energy release during the detonation cycle; as a result of the elevated gas temperature the speed of sound and consequently the gas mass velocity is also significantly increased. When the compression wave reaches the end of the intake duct and resonance chamber, which are connected to the fuel intake plenum and the decoupling chamber respectively, this pressure wave then starts to travel back in the opposite direction (fig. 4)  because it reacted against the gas mass in the plenums. This pressure wave returning to the detonation chamber is, in fact, the internal mechanism or “piston” that compresses the fuel in the detonation chamber and therefore drives the cycle. (Similar to the Kadenacy Effect). The returning pressure wave carries a part of the gas mass from the resonance and decoupling chamber, this mass now consists of heat energy and the products of detonation (CO2 and H2O).

The shock pressure wave that propagates through the gas masses is separate from the wave motion of the gas masses itself. At the start of the detonation process, large amplitude pressure wave starts immediately to travel with high velocity through both gas masses, (fig. 3) till it reaches the plenum and decoupling chamber, whilst the rapid expansion of the gas, (caused by the heat release of the detonation) is just beginning to travel away from the detonation chamber. The relatively small mass of intake duct gas will be rapidly accelerated outward behind the pressure wave, into the fuel plenum and mix with the available fuel and air in the plenum and intake duct, (fig.4) before it starts to reverse direction. Because of the larger gas mass in the resonance chamber, this gas will follow the outgoing pressure wave much more slowly. Therefore the flow reversal at the intake duct side takes place much faster, due to its smaller gas mass. (fig.5)

The timing of the detonation cycle and the resulting large amplitude pressure wave motion is determined by the lengths and geometry of the intake duct and resonance chamber. The timing of the gas mass movement is determent by the volumes and geometry of these intake and resonance sections.

The fuel detonation result in two detonation shock waves;  first into the intake duct and secondly into the resonance chamber. The wave that travels away in the intake duct side is relatively weak. Its main effect is to begin flow reversal in the intake duct itself; (fig.4) in effect it is pre-loading the intake duct section with fuel. The actual fuel loading of the detonation chamber will not begin until the major low pressure wave, resulting from the high pressure shock wave, comes back and reaches the detonation chamber. (fig.4) Once that happens, significant flow reversal begins, driven by the pressure drop in the detonation chamber, which causes the fuel to be sucked into the detonation chamber.

At this phase of the detonation cycle, there is a difference in action between the cooler and therefore more dense gas masses at the intake duct side and the hot less dense gas mass at the resonance chamber side. The intake duct gas mass now totally consists of Air/fuel mixture and therefore, Air/fuel mixture immediately begins re-filling the detonation chamber. The hot gas in the resonance chamber is also affected by the pressure drop, eventually reversing direction and is pulled back as well (fig. 5) but now the detonation chamber is filled with fuel. The resonance chamber will never be completely purged of hot detonated gases, but at reversal it will pull in hot gas masses and remnants of previous detonation cycles from the resonance chamber and the decoupling chamber, towards the detonation chamber, so the contained mass will gradually increase, while the hot detonation waves, reflected backwards by the gas masses in the decoupling chamber, move rapidly towards the already fuel filled detonation chamber. The gas density in the detonation chamber increases and compresses with the returning pressure waves (fig.6) until the pressure and temperature of the fuel in the detonation chamber reaches a value where detonation can again commence (fig.1) and the cycle repeats itself with the hot gas mass flowing again rapidly towards the resonance and decoupling chambers. This process repeats itself between 1000 and 8000 times per second.

This Thermo-acoustic HRC system has some similarities to the known “Rijke” type system. The system is basically a vessel which is open on both ends. It may seem impossible to compress gas in a vessel with both ends open, but the incredible speed of the shock compression waves from the detonation, arriving simultaneously from both sides of the open vessel collide with each other at the fuel filled detonation chamber (fig.6). This highly compressed fuel is then detonated by remnants of hot gases carried with the compression waves coming back from the resonance chamber.

The Rijke tube as it is commonly known uses the resonance chamber of the tube as the combustion chamber. Since this is a relative large volume section of the tube, and open to the atmosphere, with the reaction in the tube is considered an instable and slow combustion process.

Our design eliminates the instabilities, noise and vibration levels commonly associated with low frequency pulse combustors. Our new design and technology allows the detonation process to operate at anywhere from 500Hz to 20,000Hz (cycles per second) but more commonly between 1,000Hz and 8,000Hz depending upon the configuration and application. One of the new design features is an array of multiple, interconnecting and communicating detonation chambers, which allows us to significantly increase the unit’s overall heat output, without loss of efficiencies or increased emissions.

We now have several different HRC designs depending upon the application required. There are several other beneficial aspects of our design, including lower manufacturing costs, structural integrity and compactness.

It is important to note that as long as we maintain the basic shape and geometries of our detonation chamber design, we are able obtain additional heat output where required, by adding additional Thermo-acoustic HRC chambers.

The principal advantage of our configuration over conventional configurations is that it lends itself more readily to the joining together of separate operating modules, each module containing multiple detonation chambers. We can then regulate or adjust heat output by turning one or more of these adjoining modules on or off. This on-off capacity, which we refer to as turn-down capability, allows our unit to operate at a number of different pre-selected higher or lower output levels and frequencies while maintaining optimum heat output and heat transfer efficiencies.

We have developed our HRC system configuration for use in applications where efficiencies and emissions are a major consideration.