Application And Construction Of Wear-resistant Refractory Plastics For Circulating Fluidised Bed Boilers

Circulating fluidised bed boiler has a wide range of fuel adaptability, high combustion efficiency, can achieve the furnace desulphurisation and other outstanding features, in recent years has been rapid development. Due to the high flue gas flow rate in the circulating fluidised bed boiler, the gas carries higher coal particles and ash concentration in the circulating operation, resulting in wear and tear of the heating surface in the furnace and serious cause of frequent shutdowns, which has become a prominent problem of the circulating fluidised bed boiler.

1.1 Application parts

Taking NG.130/9.81.M circulating fluidised bed boiler as an example, the wear-prone parts of the boiler can be divided into two categories from the boiler structure. The first category for the adiabatic parts, outside the steel plate structure inside the furnace wall composed of boiler equipment, such as grinning device, separator outlet flue and other parts: the second category for the membrane wall structure, which is cooled by the furnace water or steam, and exposed to high temperatures, and contact with high coal particles, high ash, high-speed flow of flue gas structure, such as water-cooled drums under the dense-phase area and the vapour-cooled cyclone separator and other components.

Wear-resistant refractory plastic is mainly used in these pressure parts with heat conduction area, this area wear-resistant refractory material is designed as a single-layer pounding structure, fixed with wear-resistant pins, and its thickness is designed to be thin, and it is directly laid on the pipe rows on the heated surface.

Wear-resistant refractory plastic specific application parts and fixed in Figure 1.

Fig. 1 Fixing of anti-abrasive material in furnace chamber and cyclone separator and return risers

Its wear-resistant refractory plastic specific application parts and wear-resistant layer thickness is shown in Table 1.

Table 1 Wear-resistant refractory plastics in NG-130/9.81 I M circulating fluidised bed boiler application area

1.2 Intentions for the design of wear-resistant refractory plastics and their working environment

Wear-resistant refractory plastics in pressure parts wear-resistant structure application design use can be divided into wear-resistant and low-temperature insulation two kinds. From the wear-resistant point of view to consider its working environment. Wear-resistant refractory plastic application part of the working environment is detailed in Table 2.

Table 2 Working environment of abrasion-resistant and fire-resistant plastic applications

This paper introduces a commonly used wear-resistant (refractory) coroplasts provided by a refractory company, whose design performance indexes are shown in Table 3.

Table 3 Physical properties of fire and abrasion resistant plastics

The refractory wear-resistant plastic is made of corundum, kiln-converted alumina, alumina, ultra-fine micro-powder, binding agent and so on. After modulation, it is ~ a kind of mastic thick material, which is convenient for construction in various complex parts. It has the performance of hardening at room temperature, and is an air-hard material that constantly generates strength at high temperature.

3.1 Material Inspection

3.1.1 Physical - performance testing

Wear-resistant refractory plastic arrives at the construction site, the first thing to do is to carry out a sampling test of the material, testing the batch of materials of all performance indicators (including wear resistance, fire resistance, thermal conductivity, thermal shock stability, thermal expansion, shrinkage, compression and folding resistance and weight capacity, etc.). Wear-resistant (fire-resistant) plastic physical property test data are shown in Table 4.

Through the sampling test such as the material of all indicators in line with the design requirements of the boiler wall can be used in construction.

Table 4 Physical property test data for abrasion-resistant (fire-resistant) plastics

3.1.2 Construction performance testing

Wear-resistant refractory plastic construction should be tested before the construction performance of the material, mainly to check the plasticity of the material. Simple determination method is: clench the plastic with your hand, easy to pinch into glue without scattering, can be used.

3.2 Construction Requirements

Wear-resistant plastic construction procedures

Welding pin → construction surface cleaning → asphalt coating → plastic construction → plastic maintenance

 Plastic construction:

(1) Mixing:

A. Use forced mixer for mixing.

B. Before using the mixer, all the debris in the machine should be removed. If the mixing interval is long, the residue of the first mixing should be  removed before the second mixing.

(2) Construction conditions:

A. The ambient temperature of the construction site should be strictly controlled above 5℃ and below 35℃. In summer, when the ambient temperature is higher than 35℃, appropriate cooling measures are required. In case of construction in hot weather, the initial setting time is faster, and slow-setting measures can be taken. The initial setting time is controlled at 45-240 minutes.

B. The construction site should be cleared of debris before construction.

(3) Construction steps:

A. First of all, the combination of particles and fine powder using 1:1 amount with the solution for 12 hours of bundling, solution addition of 7%.

According to the next day's use. Before use, pour the bundled material into the mixer, add the binding agent and mix well, then add about 5% of the solution and mix until the colour is consistent, the amount of solution can be appropriately increased or decreased according to the climate.

B. Mixing materials can be based on the site construction progress, to determine the number of each mixing, mixing materials should be used up within 30 minutes, more time should be discarded.

C. The plastic can be pounded by hand, and the pounding tool can be wooden hammer type leather hammer, which should be pounded densely and flatly according to the designed thickness.

D. After the construction is completed, natural conservation method should be adopted, not rain.

E. In order to avoid plastic coagulation, expansion joints should be set up in parallel with the construction of plastic, horizontal expansion joints are set up as through joints, vertical joints must be staggered arrangement. Expansion joints must be set reasonably, the size of 600x600mm, expansion joints width of 2-3mm.

Lining baking process, in accordance with the flue gas flow direction (ignition duct → water-cooled air chamber → furnace → 'J' valve → separator → separator exit flue → tail flue) in the order of priority, the temperature of each region gradually rise, respectively, to the temperature of each region for the oven temperature control temperature. Furnace heating rate and constant temperature level to dense phase temperature as a control point, the cyclone separator temperature rise according to the temperature of the cyclone wall temperature measurement point of temperature control. The temperature of each area is 300 ℃ constant temperature end, then the baking temperature of the dense phase area of the furnace chamber as the monitoring temperature, continue to follow the heating curve.

Wear-resistant refractory plastic due to the thickness is small, itself and the fins on the dense pin connection to form a firm bond, after baking can be plastic from light grey to white, colour distribution is more uniform, after baking the test piece of the test piece of abrasion resistance test to achieve satisfactory results, the last must be reminded of the baking of the furnace to pay attention to the two temperature points, which are the water of crystallization and free water, if the two temperature points are not properly controlled If these two temperature points are not controlled properly, it will cause the furnace body to burst and other undesirable phenomena, please pay attention to avoid producing a loss of work.