Energy-efficient tunnel kiln design for insulating firebrick production

¶ … innovative kind of high temperature refractory and shield materials, an original top-firing system and an innovative low-mass kiln car design have been combined to create a tunnel kiln construction that can cut energy consumption and create better products. We shall employ the use of two fictional entities that have discovered an innovative solution in this area, and go about our research paper using this method.

Any company considering building a new tunnel kiln or relining a current one should keep in mind that the choice of refractory and padding materials for the kiln and kiln cars is no longer limited to time-honored thick firebrick or castable materials that soak up heat and waste energy. By graduating to structurally sound, but still lighter and more thermally efficient crop, manufacturers can slash their fuel costs and increase their bottom line (Combustion Technology Manual, 2004).

That's what Nautica Ceramics, a provider of high temperature insulating products, and kiln maker Ahura Mazda did when they joined to develop a more competent system for firing insulating firebrick (IFB) at the Nautica Ceramics plant (Combustion Technology Manual, 2004).

The project started when Nautica Ceramics wanted to build an original kiln for the manufacture of its 1500 to 2500°F grade IFB (K-20, K-23 and K-25). The kiln would restore two existing tunnel kilns built near the beginning 1960s. One functioned full time, while the other was employed as required. Each was powered by three to four large overhead burners, with smoke emitted through the roof and functioning at a great temperature of 2580°F. Both present kilns had a sidewall hot face inside layer of 8-in. thick firebrick with a thickness of 156 pounds per cubic foot (pcf) and a thermal conductivity of 12.3 BTU x in/hr x F. x ft2 at 1800°F (Southern California Gas Company, 2012). This conventional hard brick lining was supported up by 42?2-in. thick 1800°F IFB. The previous kilns had sulfur production problems, and their 1960s equipment refractory design was far from energy competent (Combustion Technology Manual, 2004). They had an expected cold face temperature of 279°F, a heat loss of 491 BTU/ft2/hr and heat storage of 68,017 BTU/ft2 (U.S. Department of Energy and Industrial Heating Equipment Association).

Nautica Ceramics was determined to restore these units with one new kiln with a manufacturing capacity approximately equal to the facility of both the previous kilns. The company required a more environmentally friendly way of starting its IFB, and it in addition needed to fit in high-tech refractory design techniques and make use of the most recent generation of insulating products (Trinks & Mawhinney, 1967).

1.3 Significance of Study

Sooner than relying on standard refractory materials, the two companies toiled together to contest materials to the operating requirements of the kiln. By making an allowance for process requirements on the IFB artifact being employed in the kiln, such as heat up, cool down, weight, duration in kiln, operating temperature and other issues, Ahura Mazda was able to plan and construct a kiln tailor-made for the modus operandi (Southern California Gas Company, 2012).

1.4 Aim

According to the technical director of Ahura Mazda the kiln system can be modified for a variety of applications and temperature ranges, giving other ceramic manufacturers to use comparable techniques and products to decrease their heat loss and power consumption. Building on the new kiln started and the innovative 290-ft long kiln was into operational in February 2002. The kiln is shielded with lightweight, energy-saving materials that reduce heat loss for the duration of its nonstop operation. Not like the old kilns that merely had 12-1/2-in (Tunnel Kilns, 2011). deep sidewalls, the walls of the new kiln are up to 29-2/4-in. thick, with a 7 in. hot face layer of 2900°F IFB that has a thickness of 65 pcf and a thermal conductivity of 3.13 BTU x in/hr x F. x ft2 at 2500°F. This product is in excess of five times more thermally proficient than the customary firebrick employed on the hot face coating in the previous kiln.

The 2900°F IFB layer is made possible by 5-1/2-in. thick 2800°F IFB, and mass fiber is squeezed in between two kinds of ceramic fiber blankets, one for the hot face and an additional one for the internal layer. The exterior wall is prepared from face brick (Matson, 2009).

Table 1. A comparison of thermal efficiencies of the old and new kiln linings.

With its structural reliability and superior thermal efficiency, the IFB demonstrated a perfect choice for the tunnel kiln purpose. By means of these lightweight resources more willingly than traditional firebrick and then backing them up with ceramic fiber materials, Nautica Ceramics presently has a kiln with a cold face temperature of 157°F in the firing area. The heat loss is a projected 146 Btu/Ft2/hr, and the heat storeroom is 33,270 Btu/ft2. The new kiln's cold face temperature and heat storage is just about half that of the old kilns, and its heat loss is under one-fourth (U.S. Department of Energy and Industrial Heating Equipment Association).

1.5 Object

The companies had to defeat several problems in creating and constructing the new kiln. For instance, the roofs in the old kilns were self-sufficient sprung-arched roofs produced from a mullite compound firebrick that was not exceptionally energy competent (Southern California Gas Company, 2012). On the other hand, the new-fangled kiln was too broad for this kind of building, so it was built with a balanced flat roof. To diminish the requirement for steel support and augment energy competence, the roof was surrounded with the same 2900°F IFB employed in the sidewalls. This structural padding fabric was poised from the roof by a hanger structure. It was supported by a 4-1/2-in. thick "R" grade ceramic fiber* with a thickness of 8 pcf (Trinks & Mawhinney, 1967).

This IFB/ceramic fiber amalgamation production made the original roof four times more energy proficient than the previous ones. Heat loss from the roofs of the previous kilns deliberated at 810 BTU/ft2/hr, while the heat loss from the roof of the novel kiln is just about 290 BTU/ft2/hr. The kiln devised team also had to discover a slim but extremely competent material to protect particular areas of the wall for the reason that the new kiln vents exhaust gas throughout hollows in its walls to a certain extent than from the roof. This is more competent than making the exhaust out through the roof. It makes the hot gases force down in the kiln, where they can help the firing procedure (Combustion Technology Manual, 2004).

1.6 Research Question

2. Literature Review

IFBs are usually employed in applications >1000°C for the reason that, at these temperatures, they present the most lucrative insulation accessible as opposed to optional insulating refractory's (Combustion Technology Manual, 2004). The structural character of the products in addition means that they present conflict to graze in high-temperature surroundings, together with chemical resistance (when the chemistry is modified to manage particular gases).

At functioning temperatures higher than 1000°C, the most imperative heat-transfer instrument becomes emission instead of conduction and convection, which are the more noteworthy heat-transfer devices at lower temperatures. The outsized pores in the cement IFB are wasteful at decreasing energy reassignment at the infrared wavelengths concerned, so this kind of IFB shows a superior thermal conductivity in comparison with the cast. On the other hand, the microporous arrangement of the cast IFB, with its minute (Southern California Gas Company, 2012) pore sizes, is a lot more efficient at altering with energy transfer at infrared wavelengths, so this category of IFB exhibits low thermal conductivity. This is why the microstructure of the cast IFB gives higher insulation in comparison to the cement IFB.

Improvements and Innovations in the New Kiln

Even though the new tunnel kiln has not been in service long, it is anticipated to considerably reduce Nautica Ceramics' general manufacturing costs. By means of a new kiln lining blueprint engineered around the energy efficient IFB and ceramic fiber items they produce, the company has slashed its energy consumption in this area by roughly 10% (Southern California Gas Company, 2012; Tunnel Kilns, 2011).

The largely tunnel kiln construction project was quite high, which included the in-house demolition work and insulating materials made by Nautica Ceramics. However the company needs a reasonably quick pay off from the projected decrease in fuel consumption (Trinks & Mawhinney, 1967; U.S. Department of Energy and Industrial Heating Equipment Association).

The IFB products fired in the innovative tunnel kiln are more reliable and have superior vigor's than those employed in the previous kiln. Initial testing shows that the typical cold crushing strength of the unit is in so far as 25% higher derived from values for a normal IFB (K-23).

3. Research Method

3.1 Data Collection

Variances in energy use as big as 38% were deliberate, under specific laboratory environments, stuck between IFBs produced by dissimilar methods.

When deciding on insulating refractory materials for furnace coatings, minute attention should be applied to the projected and delivered thermal conductivity of IFB materials (Combustion Technology Manual, 2004).

The thickness of the products must not be employed as decisive factors to review insulation aptitude, as this may initiate erroneous product choices.

To reduce energy consumption in the kiln, the available thermal conductivity ought to be calculated to an accepted international average (e.g., ASTM C-182) and be very low. Deciding on an IFB as a result of price only can turn out to be a bogus wealth and an expensive error in the future.

IFBs produced by the cast procedure present the least thermal conductivity obtainable today at submission temperatures and, consequently, offer the most energy savings.

This paper has deliberated the energy reductions that are probable by means of cast IFBs.