This point presents the history, technical aspects and advantages of the HTB-DL-WG System combined with the High Temperature Air Combustion (HiTAC) technology.

History

During the long-term cooperation between NFK company and ICS company new HTB burners (High Temperature Burners) were designed and introduced into the market. In this special burners the unique features of the HiTAC combustion technology have been successfully applied. As a result of the evolution of HTB burners the special HTB-DL-WG (High Temperature Burner for Waste Gases) burners was designed. This type of the HTB burner is designed to burn low quality fuels and utilize waste gases.

HTB-DL-WG

The HTB-DL-WG series burners are custom made for particular projects, but still share the same distinct features as: built-in staged burner throat, fuel injection directly into combustion chamber and utilization of preheated combustion air. The HTB-DL-WG burner types use the same combustion technology as the one applied in the HRS burners, however HTB burners are not equipped with regenerators. Therefore, the burners work continuously and cooperate with central recuperative systems.

The possibility of burning fuel with very low LHV (Low Heating Value) and other features of HiTAC technology are used in the special HTB-DL-WG burners. The burners are double-fuel (main and support fuel), multi-stage combustion units, capable of low and high temperature operation.

Scheme of the HTB burner with F1 and F2 mode

In this burners the HiTAC technology is realized by a high temperature mode – the so-called F2 mode. The low temperature mode (F1) is used for heating up the combustion chamber/furnace to the temperature over the fuel auto-ignition point. After that, the F2 mode is started and the burner starts to work continuously in the mixed mode (F1 and F2).

Possibility of burning low quality fuels

The possibility of burning low quality fuels (like waste gas, off gas, blast-furnace gas, etc.) is one of the HTB-DL-WG series burners features, based deeply on the general HiTAC combustion technology concept. It is well known that in order to burn the fuels, especially low quality fuels the following combustion process parameters play an important role (so-called 3xT):

• temperature (process temperature),
• time (residence time),
• turbulences (micro and large scale turbulence, including internal recirculation).

The oxygen availability at the required amount and at the correct place and time in the combustion chamber is, of course, an important issue as well.

Keeping in mind the above requirements related to the combustion technology for the combustion of low quality fuels and looking at the HiTAC combustion technology features, it is quite clear that the HTB-DL-WG burners have a natural capability of burning low quality fuels.

Temperature of the process

The HiTAC (using by HTB-DL-WG burners) is the combustion technology that it is designed to work at relatively high process temperature. The high combustion process temperature is a result of preheated air, the internal flue gas recirculation and the semi-adiabatic combustion chamber (especially important in the case of the combustion process of low heating value fuels). The process temperature is kept above the auto-ignition point of fuels (according the safety European standards over 750^oC) but at the same time below the temperature level, which are conducive to the NO_x production (below the 1,500^oC).

Residence time

One of the main features of the HiTAC concept is to apply the intensive internal flue gas recirculation, primarily to reduce the maximum available temperature in the case of the high quality fuel combustion. Since the intensive internal flue gas recirculation is applied in HiTAC, the relative high residence time is already applied in the HiTAC, which in the case of low quality fuels is an important factor. The internal flue gas recirculation, which provides the required level of the residence time, is made by high velocity of the combustion air and fuel directly injected into the combustion chamber additionally by the separated nozzles.

Turbulences

The high velocity of the combustion air and fuel forces the internal flue gas recirculation as well as the required level of the turbulence (the mixing process).

Simple injectors

Besides the above very important combustion process parameters, it is also important to point out that HTB-DL-WG burners are only equipped with simple injectors. Since the HTB-DL-WG burners use the HiTAC technology, there are not equipped with any type of typical mechanical turbulizers. The lack of the mechanical turbulizers, like for example the swirler, is additionally an important advantage in the case of the fuel contaminated by dust or by dust and moisture.

Flame stabilization

The last important HiTAC combustion technology feature is related to the way of flame stabilization, an especially important issue in the case of low heating value fuels. In the HiTAC combustion technology there is no stabilization in the sense of the typical combustion technology. The combustion process takes place in the whole combustion chamber on the required temperature level over the auto-ignition point. The mixing process is forced by high velocity injection of the combustion air and fuel.

All the above pointed out features make the HTB-DL-WG burners using HiTAC technology very suitable for the combustion of low quality fuels and insensitive to a wide range of the waste gas parameters like composition, pressure, temperature and flow rates. Additionally, the HTB-DL-WG burners can be applied in wide range of applications from small-size units (about 0.1 MW) to very large scale units (about 20.0 MW).

HiTAC clean combustion

In HTB-DL-WG appliances the HiTAC technology employs volume combustion, combustion air preheat and staged fuel injection to achieve main goals of combustion stability and quality with minimal energy input from support fuel.

The HiTAC combustion technology principle requires fuel and preheated combustion air to be injected at high velocities directly into combustion chamber. Injection points alignment is a crucial factor, burner throat and fuel nozzles are located in a custom made burner tile.

Through injection velocity and injection points placement intense mixing of combustion chamber contents takes place. This desirable effect creates a specific, low oxygen combustion environment.

HiTAC combustion technology at work

B: F: A: H: BA: BH: (*):

Burnt Gas Fuel Air Highly-preheated Air Mixture of B and A Mixture of B and H Combustion

Due to intense mixing and oxygen deficient environment of HiTAC chamber conditions “volumetric” combustion process takes place results in complete, clean, low NO_x (about 50 ppm) burning of fuels supplied.

Efficiency and emissions

Industry experience acknowledges excellent combustion capabilities and wide fuel compatibility of the HTB-DL-WG burners. One of typical industrial application of the HTB-DL-WG burners is copper blast furnace waste gas utilization system cooperating with steam boiler where especially the high thermal efficiency (about 82%) of the system can be observed.

Scheme of the Waste Gas Utilization System cooperating with steam boiler – one of the typical application of the HTB-DL-WG burners

Pollutant emissions remain very low throughout various applications due to controlled combustion process. Significant reduction in NO_x emission can be observed in most cases. Also combustion chamber refractory lifetime is extended due to better combustion characteristics and temperature distribution in the chamber.