Honeycomb ceramic heat storage body is developed according to the actual combustion condition of heating furnace in our country. In regenerative combustion system normal work, in the process of ceramic honeycomb regenerator periodically contact with high temperature flue gas and combustion air or gas under normal temperature, through the heat storage and heat regenerator, the high temperature flue gas heat passed on to the normal temperature of combustion air or gas, realize the limits of waste heat recovery and normal temperature combustion-supporting air or gas high temperature preheating, achieve the goal of high efficiency and energy saving. It can be seen that the safe and stable operation of honeycomb ceramic heat storage body and the high intensity heat transfer effect are the key factors affecting the high efficiency and energy saving of regenerative combustion technology. Therefore, the requirement of material performance is analyzed from two aspects: physical and chemical properties that affect the stable operation of heat storage body and thermal and physical properties that affect heat transfer effect.

I. physical and chemical performance requirements of honeycomb ceramic heat storage material

    For regenerative reheating furnace, honeycomb ceramic heat storage is required to work for a long time under the condition of high temperature, iron oxide dust and frequent temperature fluctuation.

1. Fire resistance

    For regenerative combustion system, the preheating temperature efficiency of combustion air or gas is high, and generally it can reach the level of 100-200℃ lower than the flue gas temperature, so the honeycomb ceramic heat storage body works in the high temperature for a long time, so it has the requirement of fire resistance. For the general small billet reheating furnace, the temperature of flue gas is 1250-1300℃, for the high temperature large billet reheating furnace, the temperature of flue gas can reach 1400℃, or even higher, so it can be seen that different application conditions have different requirements on the refractory of honeycomb ceramic reheater.

2. Thermal shock stability

    According to the heat transfer process of the regenerator, and honeycomb ceramic regenerator is running for a long time, under the condition of heating and cooling temperature at the surface and internal intercropping cyclical changes at any time, if the thermal shock resistance of regenerator could not reach the requirements of a certain, will be under the influence of frequent alternation of heat bilges cold shrink, cause the regenerator broken and blocked air flow channel, increase the pressure loss, influence of regenerator heat effect, serious when will cause the regenerator can not work normally, were forced to change regenerator. According to the nature of the refractory material of the higher density, the greater the thermal expansion coefficient, the thermal shock stability, at the same time, the high density of the material, its density is compared commonly big, heat storage capacity is big, therefore, when choosing formula of the heat storage material, should be on the premise of guarantee the material thermal shock stability, improve the density as much as possible.

3. Structural strength

    Regenerator is by a single regenerator layering and points have been assembled, under the condition of high temperature in the actual work, the honeycomb ceramic regenerator bottom to upper and under its own weight, therefore, required regenerator must have enough high temperature compressive strength and creep resistance, otherwise, will lead to deformation of regenerator and broken, make gas flow resistance increases, in thermal efficiency decline, and even affect the safe operation of the regenerative combustion system. At the same time, under the action of high temperature dust and gas high speed scour, it is easy to cause the hole wall wear and defect peel damage of the heat storage body, so it is required that the heat storage body has high high temperature structural strength and softening temperature under load. According to experience, the long-term working temperature of refractory is generally 100℃ lower than its softening temperature under load.

4, slag resistance

    Because the furnace gas in the heating furnace contains iron oxide dust, through the contact with refractory and high temperature solid reaction, the formation of low melting point material, reduce the soft melting temperature of the material. Caused as a result, in the process of normal use, low melting point material adhesion of hole wall, increasing the gas flow resistance, reduce the regenerator in thermal efficiency, at the same time, low melting point of hole wall material adhesion, enhances the hole wall of dust capture ability, promote the process dust adhesion of hole wall, further worsen the performance of the regenerator caused extensive congestion even regenerator hole, cause the regenerator can't work normally. Therefore, thermal storage materials must also have a good corrosion resistance to iron oxide.

Requirements for thermophysical properties of honeycomb ceramic regenerator materials

    Important performance index of the regenerator is E temperature efficiency and heat recovery efficiency of eta, the specific calculation formula is:

Temperature efficiency E=T"a-T'a/T'y-T'a×{bfb}

    Where, T'a and T"a are the average temperature of preheated air inlet and outlet, ℃; T'y is the flue gas inlet temperature, ℃.

Heat recovery efficiency of eta = Q "a - 'a/Q Q y x {bfb}

Where, Q'a and Q"a are the enthalpy of the inlet and outlet of preheated air, kJ/h; Q'y is the enthalpy of flue gas inlet, kJ/h.

    According to the above formula can be seen, temperature efficiency and heat recovery efficiency E eta is comprehensive characterization of regenerator heat transfer process, as a heat transfer process of ceramic honeycomb regenerator, the thermal physical properties on the have important influence.

1. Specific heat capacity

    Specific heat capacity c reflects the temperature change caused by the accumulation of certain heat inside the material. For materials with the same mass and different c, when they absorb the same heat from the outside world, their characteristic value - temperature is different. In the process of heat transfer, the material with a large c value has a large temperature difference with the heat-carrying medium and an increased heat exchange capacity. Compared with the material with a small c value at the same temperature, the material with a large c value accumulates more heat.

2. Material thermal conductivity

    In the process of heat absorption and heat release of honeycomb ceramic regenerator, the heat transfer resistance will directly affect the heat transfer efficiency of the regenerator. The thermal conductivity of a material is a physical property of how easy it is for a material to transfer energy. In materials with high thermal conductivity, heat is transferred quickly from surface to center or from inside to surface. According to Newton's complex heat transfer formula, the interface comprehensive heat transfer coefficient of the heat storage body and gas in heat transfer process a:

A = (1 / alpha + S/lambda) - 1

    Where, alpha is the convection heat transfer coefficient between gas (air or flue gas) and heat accumulator (honeycomb ceramic heat accumulator), W/(m2·K); S is the average distance of heat flow inside the solid of the regenerator, m; Lambda is the thermal conductivity of the regenerative material, W/ m lambda.

    The formula shows that the material lambda value is high, the comprehensive heat transfer coefficient a increases; The heat transfer speed is fast, the heat exchange increases; The temperature efficiency E value of regenerator increases, which is beneficial to the miniaturization of equipment and the arrangement and installation of equipment.

3. Emissivity of honeycomb ceramic heat storage material

    Due to the high working temperature of honeycomb ceramic regenerator, the heat in the flue gas is transferred to the regenerator by convection and radiation. According to the radiation exchange heat treatment between the two gray bodies where the flue gas fills the entire gap of the regenerator, the resulting radiation coefficient is Cd:

Cd C0 = (1 / + 1 / epsilon epsilon 1-1) - 1

    Where, C0 is the blackbody radiation coefficient, C0= 5.67w /(m2·K4); Epsilon and epsilon 1 are the emissivity of heat storage material and the emissivity of flue gas. It can be seen from the formula that Cd has a positive correspondence with the emissivity of the regenerator material. Therefore, increasing the emissivity of the material of the heat storage body, or taking measures to increase the emissivity, can increase the value of Cd, so as to strengthen the high temperature radiation heat transfer.

4, density

    For sensible heat storage materials, the greater the density, the greater the weight of the material per unit volume. Under the condition of the same specific heat capacity, the weight of the regenerative material absorbing the same amount of heat is the same, so the material with high material density can reduce the volume of the regenerative chamber. Under the condition of rated heat storage of the regenerative chamber, the regenerative material with high volume density is adopted, and the volume of the regenerative chamber is small, which is convenient for the installation and arrangement of the regenerative combustion system. Therefore, high density materials should be selected as far as possible when selecting honeycomb ceramic heat accumulator.