crushing plant for refractory bed material

recycling of refractory bricks used in basic steelmaking: a review - sciencedirect

Despite technical feasibility, high value refractory recycling remains limited.Technological advances such as automated sorting can overcome recycling barriers.Cooperation between producers and recyclers is required to optimize recycling.Supply risk and rising prices create an opportunity for increased recycling.

Refractories are indispensable for all high temperatures processes, such as the production of metals, cement, glass and ceramics. It is estimated that up to 28 million tons of spent refractories are generated every year. Despite these significant amounts, recycling of spent refractories has received little attention due to the abundance of low cost virgin raw materials and low disposal costs of the, largely inert, materials. In the last two decades, recycling of spent refractories has started to receive more attention due to environmental considerations and increasing costs for landfilling. However, recycling in applications such as road bed foundations or slag conditioners does not capture the full intrinsic value of the materials. Higher value recycling as refractory raw materials is much more limited, and estimated at only 7% of refractory raw material demand. Recently, rising prices and supply issues for high quality virgin raw materials have created a strong incentive for closed-loop refractory recycling. This review gives an overview of the history of refractory recycling and the main refractory recycling applications, with a particular focus on recycling in new refractories. Current spent refractory processing in view of raw material recycling is discussed, and an outlook is given to future trends and developments.

refractory failure elimination in fludised bed reactors turkish forum english

Dr Tom Honeyands BHP Billiton Newcastle Technology Centre Dr Andrew Shook BHP Billiton Newcastle Technology Centre Dr Philip Clausen School of Engineering, University of Newcastle Executive Summary Spalling of fluidised bed reactor refractories and subsequent feed leg blockages have been a significant cause of lost production in Iron, alumina and nickel processing plants. This work describes the Strategic Refractory Management Plan developed to address high refractory failure rates during the first years of operation of the Port Hedland HBI plant. An example is then given of a mathematical modelling study of the heat transfer and stresses in the reactor vessel to see whether any conclusions can be drawn about the maximum allowable heating or cooling rates. The reactor hot face refractory and insulation layers, restrained by a stainless steel shell, were modelled using strand7 finite element software. Here only the dome of a simplified reactor, not including expansion joints, anchors, gas inlets and outlet, was modelled to determine the stress profile through the wall when subject to thermal loading. Several alternative refractory configurations were considered for this application. The compressive thermal stresses predicted on heat-up were found to always be lower than the crushing strength of the materials in this investigation, and no conclusions can be made regarding maximum heating rate. When the internal surface of the reactor is cooled by cold purge gasses, tensile stresses can potentially be generated in the hot face refractory, along with shear stresses between the hot face and the insulation. Tensile stresses were only predicted in one case 150mm hot face / 150mm insulation during rapid cooling. This configuration was therefore rejected. Shear stresses in the other refractory configurations were found to be relatively low (<1.1MPa). No indications of the reasons for previous refractory failures were found using this simple model. It is concluded that differences in the dry-out and curing of the 60% Alumina and 80 % Alumina based castables hot face refractories is responsible for their differing performance. Introduction In this paper we consider the example of BHP Billitons hot Briquetted iron (HBI), processing plant in Port Hedland due to problematic processing characters. In this plant the high alumina refractories must contain abrasive solids at elevated temperatures and pressures under reducing gas conditions. A combination of reasons accelerated the deterioration and shortened the life expectancy of the refractories during this period. The following examples are typical of the problems experienced:

Spalling of fluidised bed reactor refractories and subsequent feed leg blockages have been a significant cause of lost production in Iron, alumina and nickel processing plants. This work describes the Strategic Refractory Management Plan developed to address high refractory failure rates during the first years of operation of the Port Hedland HBI plant.

An example is then given of a mathematical modelling study of the heat transfer and stresses in the reactor vessel to see whether any conclusions can be drawn about the maximum allowable heating or cooling rates.

The reactor hot face refractory and insulation layers, restrained by a stainless steel shell, were modelled using strand7 finite element software. Here only the dome of a simplified reactor, not including expansion joints, anchors, gas inlets and outlet, was modelled to determine the stress profile through the wall when subject to thermal loading.

Several alternative refractory configurations were considered for this application. The compressive thermal stresses predicted on heat-up were found to always be lower than the crushing strength of the materials in this investigation, and no conclusions can be made regarding maximum heating rate.

When the internal surface of the reactor is cooled by cold purge gasses, tensile stresses can potentially be generated in the hot face refractory, along with shear stresses between the hot face and the insulation. Tensile stresses were only predicted in one case 150mm hot face / 150mm insulation during rapid cooling. This configuration was therefore rejected.

Shear stresses in the other refractory configurations were found to be relatively low (<1.1MPa). No indications of the reasons for previous refractory failures were found using this simple model. It is concluded that differences in the dry-out and curing of the 60% Alumina and 80 % Alumina based castables hot face refractories is responsible for their differing performance.

In this paper we consider the example of BHP Billitons hot Briquetted iron (HBI), processing plant in Port Hedland due to problematic processing characters. In this plant the high alumina refractories must contain abrasive solids at elevated temperatures and pressures under reducing gas conditions. A combination of reasons accelerated the deterioration and shortened the life expectancy of the refractories during this period. The following examples are typical of the problems experienced:

Cracking, spalling and or even complete failure of reactor refractories causes significant lost of production, increased maintenance and increased operational costs. These refractory failures can be caused by:

Incorrect material selection: Refractories must be chosen with the correct thermo-physical properties including thermal conductivity, coefficient of thermal expansion, strength and chemical compatibility with the process stream.

To address this problem, a technical team supervised by Genghis Erkan developed a long term Strategic Refractory Management Plan in BHP Billiton, to systematically solve refractory and related problems. This plan provided systematic material selection and evaluation process and enabled us to manage and monitor such things as uniformity of heat transfer during start-up, operation and shut down.

This resulted in longer campaign periods, less equipment wear, shorter shut-downs and decreased overall operating costs. The resulting benefits can be seen in the later years of operation shown in Table 1. The corresponding increase in refractory life is shown in Table 2.

Design modifications in some critical areas to improve refractory life, such as briquetting feed bin striker pad, reactor dome refractories re-design, replacing panels with a continuous ring and Implementation of an effective monitoring system

Development of suitable heat up procedures to remove all free and molecular moisture and chemical binder, relieving stresses in the structure, promoting uniformity of thermal conductivity and minimising the impact of porosity on the system

To assist with the modification to the refractory design, and to guide changes to start up and operating strategy, a number of mathematical models were used. In conjunction with this, the failures of the refractory lining were extensively studied during post mortem investigations, Historical plant data were analysed to determine refractory performance relative to operating conditions, and in service tests were carried out.

The temperature profiles through the refractory were calculated using a commercial heat transfer package, Heating, using the thermal properties of the refractories supplied by the plant technology department and assuming that the thermocouple present in the gas space of the reactor vessel was a good approximation to the hot face temperature, and applying external convective heat transfer. An example of the temperatures calculated through the refractory thickness is given in Figure 2.

When the reactor is cooled due to process upsets, the internal surface of the hot face can be cooled below the temperature at the hot face / insulation boundary (see Figure 3). This sub-cooling has the potential to generate tensile stresses in the hot face refractory and shear between the hot face and insulation. These stresses are calculated in the next section.

A finite element model of the dome of the reactor was created to determine the stress profile through the reactor wall when subject to the thermal loading calculated in Section 4.1. The reactor consists of a 20mm thick, 3740mm internal diameter stainless steel cylinder with a hemispherical dome cap. The internal surface of the shell is coated with insulation refractory with this coated with hot face refractory. The normal configuration has 200mm of insulation and 100mm of hot face.

To analyse the thermally induced stress in the upper wall section of the reactor requires a full 3D model to be built and solved. Ignoring the two nozzles in the reactors dome section, however, simplifies this structure to a solid of revolution. Here a planar section through the wall can be modelled to represent the complete stress field in the structure as long as this section can be extruded 360 around an axis to create the structure.

Modelling the dome as a solid of revolutions also requires the material properties, loading and constraints to be axisymmetric in nature, that is, they are circumferentially independent. Here we assumed all material properties to be isotropic with the lower edge of this section of the bin restrained from moving in the axial direction only.

Figure 4 shows the finite element model of the simplified dome of the reactor vessel. The model consists of just over 5000 low-order plate elements with the red, blue and green coloured elements modelling the hot-face refractory, insulation refractory and stainless steel respectively. Nodes on the lower edge of the cylindrical section were constrained from moving in the axial (y) direction. The material properties used for the stainless steel, insulation and hot-face are given in Table 3.

Early modelling work showed that the internal surface of the hot face was always in compression for the entire temperature cycle. Here it was assumed that the zero stress state occurred at 40C, the ambient air temperature. This assumption, however, may be in error as the hot face refractory was cured at a temperature significantly above ambient. As such, the temperature profile through the wall during the curing process is more likely to coincide with the zero stress state. At this zero stress state, the modelling has indicated that tensile stress will occur on the internal surface of the hot face refractory.

Table 4 below shows the maximum compressive stress and the shear stress at the interface of the insulation refractory and hot face refractory during the heat-up period and into the early cool down part of the bins operating cycle. As expected, the maximum stress for all times considered occurred on the plate element adjacent to the inside surface of the hot face refractory. The shear stress rz, shown in Table 4 was the value at the centroid of the hot face element adjacent to the boundary. As can seen, the value of the shear stress is small in comparison to the normal stresses.

Zero Stress State at a Wall temperature of 550C Figure 3 and 4 show contours of circumferential stress for the 200,000s and 350,000s respectively with the wall temperature at 550C. As can be seen, figure 5 shows compressive stresses in the element adjacent to the inside surface of the hot-face with the other two recording tensile stress. The centroid stress is shown in Table 4. Figure 3. Contours of stress at 200,000s with an internal temperature of 550C. Figure 4. Contours of stress at 300,000s with an internal temperature of 550C. Table 5. Stress at the centroid of the plate indicated in figure 3 for the 550C zero stress state. Time (sec) r MPa z Mpa MPa rz, MPa 167000 -6.08 -0.0023 -6.08 0.035 200000 3.56 -0.017 3.56 -0.042 300000 15.8 -0.073 15.8 -0.107 Zero Stress State at a Wall temperature of 700C Table 6 documents the stress for the case 167,000s and 200,000s. Results for the 300,000s case was not considered, as these stresses will simply be higher than for the case at 200,000s. Table 6. Stress at the centroid of the plate indicated in figure 6 for the 700C zero stress state. Time (sec) r MPa z MPa MPa rz, MPa 167000 1.41 -0.077 1.41 -0.018 200000 10.96 -0.137 10.97 -0.086 Stresses in Different Refractory Thickness As previously stated, the normal wall had 200mm of insulation refractory and 100mm of hot face. Here two other configurations are considered: 150 mm of insulation and 150mm of hot face and 50mm insulation and 150mm of hot face. The zero stress state was assumed to be at 40C. Temperature profiles through the wall were supplied. The results show for the 150mm hot face/ 50mm insulation case the refractory is in compression at both 200,000s and 300, 000s as indicated in Table 7. The shear stress at the hot face/insulation junction is shown in the last column in the table. For the 150mm hot face /150mm insulation case, however, the plate element adjacent to the inside surface is in tension as shown in Table8. Here the shear stress at the hot face /insulation junction is of similar magnitude to that in the 150mm hot face/50mm insulation case. The tensile stress at the surface of the hot face suggests that this insulation/hot face configuration is undesirable. Table 7. Normal stresses at the centroid of the plate adjacent to the inside surface of the hot face and the shear stress at the hot face insulation boundary for 150mm hot face /50mm insulation case. Time (sec) r MPa z MPa MPa rz, MPa (interface) 200000 -16.0 -0.095 -16.0 0.081 300000 -7.55 -0.045 -7.55 0.038 Table 8. Normal stresses at the centroid of the plate adjacent to the inside surface of the hot face and the shear stress at the hot face insulation boundary for 150mm hot face /150mm insulation case. Time (sec) r MPa z MPa MPa rz, MPa (interface) 200000 13.54 -0.017 13.55 -0.052 300000 7.4 -0.018 7.5 -0.028 Discussion The heat-up rate used in Figure 2 is extremely high, as the gas thermocouple has essentially been set instantaneously to 700C. The state of stress in the bin is generally compression in the refractory with the stainless steel shell in tension. Even at this extreme heating rate, the compressive stresses in the refractory do not exceed the crushing strength of either 60% Al2O3 or 80% Al2O3 refractories where the crushing strength is between 68 and 72MPa. These stresses were calculated for the three refractory configurations: 100 mm hot face / 200 mm insulation: The internal surface remains in compression, with small amounts of shear at the interface 150 mm hot face / 150 mm insulation: The internal surface goes into tension, suggesting that the refractory will crack during cooling in this case. 150 mm hot face / 50 mm insulation: The internal surface remains in compression, with small amounts of shear at the interface. In this case there is essentially no sub-cooling of the internal surface, suggesting that this configuration will be the most resistant to thermal stresses on cooling. The wall temperature would increase from approximately 85C to 180C, and the heat losses would increase from approximately 80kW to 185kW with this configuration. This heat loss is still small in comparison to the other losses through briquetting. During the thermal analysis a simple comparison was made between 60% Al2O3 and 80% Al2O3. Analysis of historical data by plant suggests that the performance of 60% Al2O3 has been superior to that of 80% Al2O3. A simple measure of thermal shock resistance, based on avoiding the initaition of fracture, can be calculated using the following equation. The results of the comparison between 60% Al2O3 and 80% Al2O3 using Equation (1) are given in Table 9. The termal shock resistance, R, is given by: R = k..(1-) / E.a (1) Where; R is Thermal shock resistance k is the thermal conductivity, is the failure stress, E is Youngs modulus (value of 4.8 Gpa used), a is the coefficient of thermal expansion, and is Poissons ratio (value of 0.3 used). Table 9. Simple comparison of thermal shock resistance of 60% Al2O3 and 80% Al2O3. 60% Al2O3 80% Al2O3 K (W/m.K) 0.92 1.56 (MPa) 6 16 a (mm/mmC) 8.5 x 10-6 7.0 x 10-6 R 95 520 This comparison suggests that 80% Al2O3 should have better thermal shock resistance than 60% Al2O3 refractories, which is presumably why it was used. There is clearly some other reason for the differences in performance. One possibility is that differences may exist in the behaviour of the two refractories during dry out and curing. 80% Al2O3 is a wet gunning mix, whereas 60% Al2O3 is a dry gunning mix. Both are reportedly dried out using the same temperature ramps and holds (up to 550C). This was explored using special stress model, by changing the temperature at which the refractory was at a zero stress state from room temperature to 550C. This assumes that the castable refractories form their bonds at the curing temperature of 550C. Heating above this temperature puts the refractory into compression as before, however, cooling below this temperature puts the internal surface of the refractory into tension and could lead to failure. This hypothesis is likely to be generally correct, in that large thermal cycles are bad for the refractories and that the reactor should be kept at its operating temperature whenever possible. Other more quantitative predictions cannot be made with our current level of knowledge. Conclusions The establishment of a Strategic Refractory Management Plan resulted in a significant increase in refractory life at the Port Hedland HBI plant, and a corresponding decrease in refractory management costs. A mathematical modelling study was carried out as part of this plan. The finite element modelling indicated that if the zero stress state was assumed to be at an ambient temperature of 40C, then the stress in the refractory wall was compressive at all times during a typical operating cycle. If, however, the zero stress state was set at the refractory curing temperature, then the stress within the refractory wall maybe tensile. Furthermore, raising the refractory curing temperature can lead to tensile stress in a greater percentage of the operating cycle. This led the refractory engineers to closely examine the drying and curing of refractories, and led to improved practices. The refractory wall with a 150 mm hot face/150 mm insulation configuration produces tensile stress on the inside surface of the hot face irrespective of the temperature of the zero stress state. These results suggest that this thickness combination is inappropriate for a refractory vessel. To achieve the best results for the plant a proper evaluation is best accomplished by complete cooperation and communication between refractory manufacturer, installer, and internal stakeholders. To continue to operate the plant without a Strategic Refractory Management Plan will prove to be very costly and unsustainable. References Genghis Erkan, BChEng, MscEnv, MIEAust, CPEng, MIREng Fludised Bed Reactor Refractory Implementation Strategy, 2003. Dr P.D Clausen, BE, PhD, A Finite Element Analysis of the Refractory Wall, 2001. Dr Andrew Shook, BHP Billiton Technology Internal report, Thermal Stress Analysis of BFB Refractories, 2001. Dr Tom Honeyands, BHP Billiton Technology Internal Report, Thermal Stress Analysis of BFB Refractories, 2001.

Figure 3 and 4 show contours of circumferential stress for the 200,000s and 350,000s respectively with the wall temperature at 550C. As can be seen, figure 5 shows compressive stresses in the element adjacent to the inside surface of the hot-face with the other two recording tensile stress. The centroid stress is shown in Table 4.

As previously stated, the normal wall had 200mm of insulation refractory and 100mm of hot face. Here two other configurations are considered: 150 mm of insulation and 150mm of hot face and 50mm insulation and 150mm of hot face. The zero stress state was assumed to be at 40C. Temperature profiles through the wall were supplied.

The results show for the 150mm hot face/ 50mm insulation case the refractory is in compression at both 200,000s and 300, 000s as indicated in Table 7. The shear stress at the hot face/insulation junction is shown in the last column in the table.

For the 150mm hot face /150mm insulation case, however, the plate element adjacent to the inside surface is in tension as shown in Table8. Here the shear stress at the hot face /insulation junction is of similar magnitude to that in the 150mm hot face/50mm insulation case. The tensile stress at the surface of the hot face suggests that this insulation/hot face configuration is undesirable.

Table 8. Normal stresses at the centroid of the plate adjacent to the inside surface of the hot face and the shear stress at the hot face insulation boundary for 150mm hot face /150mm insulation case.

The heat-up rate used in Figure 2 is extremely high, as the gas thermocouple has essentially been set instantaneously to 700C. The state of stress in the bin is generally compression in the refractory with the stainless steel shell in tension. Even at this extreme heating rate, the compressive stresses in the refractory do not exceed the crushing strength of either 60% Al2O3 or 80% Al2O3 refractories where the crushing strength is between 68 and 72MPa.

150 mm hot face / 50 mm insulation: The internal surface remains in compression, with small amounts of shear at the interface. In this case there is essentially no sub-cooling of the internal surface, suggesting that this configuration will be the most resistant to thermal stresses on cooling. The wall temperature would increase from approximately 85C to 180C, and the heat losses would increase from approximately 80kW to 185kW with this configuration. This heat loss is still small in comparison to the other losses through briquetting.

During the thermal analysis a simple comparison was made between 60% Al2O3 and 80% Al2O3. Analysis of historical data by plant suggests that the performance of 60% Al2O3 has been superior to that of 80% Al2O3. A simple measure of thermal shock resistance, based on avoiding the initaition of fracture, can be calculated using the following equation.

This comparison suggests that 80% Al2O3 should have better thermal shock resistance than 60% Al2O3 refractories, which is presumably why it was used. There is clearly some other reason for the differences in performance. One possibility is that differences may exist in the behaviour of the two refractories during dry out and curing. 80% Al2O3 is a wet gunning mix, whereas 60% Al2O3 is a dry gunning mix. Both are reportedly dried out using the same temperature ramps and holds (up to 550C).

This was explored using special stress model, by changing the temperature at which the refractory was at a zero stress state from room temperature to 550C. This assumes that the castable refractories form their bonds at the curing temperature of 550C. Heating above this temperature puts the refractory into compression as before, however, cooling below this temperature puts the internal surface of the refractory into tension and could lead to failure.

This hypothesis is likely to be generally correct, in that large thermal cycles are bad for the refractories and that the reactor should be kept at its operating temperature whenever possible. Other more quantitative predictions cannot be made with our current level of knowledge.

The establishment of a Strategic Refractory Management Plan resulted in a significant increase in refractory life at the Port Hedland HBI plant, and a corresponding decrease in refractory management costs.

A mathematical modelling study was carried out as part of this plan. The finite element modelling indicated that if the zero stress state was assumed to be at an ambient temperature of 40C, then the stress in the refractory wall was compressive at all times during a typical operating cycle. If, however, the zero stress state was set at the refractory curing temperature, then the stress within the refractory wall maybe tensile.

Furthermore, raising the refractory curing temperature can lead to tensile stress in a greater percentage of the operating cycle. This led the refractory engineers to closely examine the drying and curing of refractories, and led to improved practices. The refractory wall with a 150 mm hot face/150 mm insulation configuration produces tensile stress on the inside surface of the hot face irrespective of the temperature of the zero stress state. These results suggest that this thickness combination is inappropriate for a refractory vessel.

To achieve the best results for the plant a proper evaluation is best accomplished by complete cooperation and communication between refractory manufacturer, installer, and internal stakeholders. To continue to operate the plant without a Strategic Refractory Management Plan will prove to be very costly and unsustainable.

jainco refractories

JAINCO Group of Companies initiated its functioning in the field of refractories in the year 1984, establishing its first manufacturing unit at Alwar, Rajasthan (India), followed by VKIA - Jaipur RIICO, Bagru in Rajasthan (India) and Wankaner, Gujarat (India).

Jainco has been India's premier manufacturer of Refractory Bed Material for Atmospheric Fluidized Bed Combustion (AFBC) and Circulating Fluidized Bed Combustion (CFBC) Boilers since the introduction of this Fluidized Bed Technology in India in the early 1980s. We have a mature working relationship with the worlds leading boiler manufacturers (most notably, BHEL, Thermax Babcock & Wilcox, ISGEC & CVL) and a very wide base of captive power-plant customers. Since 35 years of its inception, Jainco has supplied unsurpassed materials to diverse industries - Power & Energy, Cement, Textiles, Paper, Construction, Iron & Steel, Chemicals & Fertilizers and Engineering etc.

Our industry alliances have enhanced our knowledge and technical know-how about critical applications of refractories for various industries. Continuous in-house improvements based on exhaustive feedback and interactions with our customers and boiler operators are the foundations that have made our products a technical and commercial success. With the world moving towards cleaner sources of energy, our company has developed a unique & an exclusive type of Bed Material for biomass-fired boilers.

For over 35 years, Jainco has built a reputation for high-performing refractory products and a focus on quality controls has been a major key to the success of our refractory works at customer sites around the world.

Process Quality Control: Jainco products are a result of in-house manufacturing and the use of highest quality raw materials. The Bed material processed from high temperature pure refractory aggregates is screened multiple times to eliminate undesired coarse and fine particles thereby obtaining perfect particle size distribution. Our powerful rare-earth magnetic separators ensure minimal iron percentage, resulting in top notch quality products.

Each of our dispatch and delivery is accompanied with a Test Certificate report signed by the respective quality control manager. Packaging needs are taken care of specific to each product and delivery method, ensuring that the products reach you in top shape.

We boast of state of the art machinery, proficient in-house laboratories and nurture alliances with the best transport & packaging companies for quality and timely delivery of your shipments. Our auxiliary services are perfectly in place to ensure a quality product, packaging, delivery and tracking up to your factory.

We take pride in having a multi-location set up in the heart of the industrial hub of our country. We are the only company in the country that can supply most of its product range from two different geographical locations, ensuring complete backup in force majeure incidents.

crushing plant - an overview | sciencedirect topics

A crushing plant delivered ore to a wet grinding mill for further size reduction. The size of crushed ore (F80) was. 4.0mm and the S.G. 2.8t/m3. The work index of the ore was determined as 12.2kWh/t. A wet ball mill 1m 1m was chosen to grind the ore down to 200 m. A 30% pulp was made and charged to the mill, which was then rotated at 60% of the critical speed. Estimate:1.the maximum diameter of the grinding balls required at the commencement of grinding,2.the diameter of the replacement ball.

A 1.0 1.5m ball mill was loaded with a charge that occupied 45% of the mill volume. The diameter of balls was 100mm. The mill was first rotated at 25rpm. After some time, the rotation was increased to 30rpm and finally to 40rpm. Determine and plot the toe and head angles with the change of speed of rotation.

A 2.7m 3.6m ball mill was filled to 35% of its inner volume. The charge contained 100mm diameter steel balls. The mill was rotated at 75% of critical speed. The ore size charged was 2.8mm and the product size (P80) of 75 m. The work index of the ore was 13.1kWh/t. Determine the production rate of the mill when operated under wet conditions.

Hematite ore of particle size 4000 m is to be ground dry to 200 m (P80). The work index of the ore was determined and found to be equal to15.1kWh/t. Balls of diameter 110mm were added as the grinding media. The mill was rotated at 68% of the critical speed and expected to produce at the rate of 12t/h. The combined correction factors for Wi equalled 0.9. Calculate:1.the volume of the mill occupied by the grinding media,2.the mill capacity when the mill load was increased by 10% of its original volume.

The feed size of an ore to a 1.7m 1.7m wet ball mill operating in closed circuit was 5000m. The work index of the ore was determined under dry open circuit conditions and found to be 13.5kWh/t. The mill bed was filled to 30% of its volume with balls of density 7.9t/m3. A 20:1 reduction ratio of ore was desired. The mill was operated at 80% of the critical speed. Assuming a bed porosity of 40%, estimate the mill capacity in tonnes per year.

A ball mill is to produce a grind of 34 m (P80) product from a feed size of 200 m at a rate of 1.5t/h. The grinding media used was 90% Al2O3 ceramic ball of S.G. 3.5. The balls occupied 28% of the mill volume. The mill was rotated at 65% of the critical speed. The work index of the ore was 11.3kWh/t. Estimate the size of the mill required.

A wet overflow ball mill of dimensions 3.05m 3.05m was charged with nickel ore (pentlandite) of density 4.2 having a F80 value of 2.2mm. The mass of balls charged for grinding was 32t, which constitutes a ball loading of 35% (by volume). The mill was rotated at 18rpm. Estimate:1.power required at the mill shaft per tonne of ball,2.power required at the mill shaft when the load (% Vol) was increased to 45%.

A grate discharge mill of dimensions 4.12m 3.96m was loaded to 40% of its volume with gold ore. The mill drew 10.95kW power per tonne of balls. To grind the ore to the liberation size the mill was run at 72% of the critical speed when charged with balls 64mm in size and 7.9t/m3 density. Determine:1.the fraction of the mill filled with balls,2.the mass of balls charged.

The feed size to a single stage wet ball mill was 9.5mm of which 80% passed through a 810 m sieve. The mill was expected to produce a product of 80% passing 150 m. The feed rate to the mill was 300t/h. The ball mill grindability test at 65 mesh showed 12kWh/t. The internal diameter of the ball mill was 5.03m and the length-to-diameter ratio was 0.77. The steel balls occupied 18% of the mill. The total load occupied 45% of the mill volume. If the mill operated at 72% of the critical speed, determine:1.the mill power at the shaft during wet grinding,2.the mill power at the shaft during dry grinding.

A 5.5m 5.5m ball mill is lined with single wave liners 65mm thick, which cover the entire inside surface. The centre line length was 4.2m and the trunnion diameters 1.5m in diameter. The mill was charged with an ore and 100mm diameter steel balls as the grinding media so the total filling of the cylindrical section was 40% and the ball fractional filling was 0.15 %. The slurry in the mill discharge contained 33% solids (by volume). The mill was expected to rotate at 12.8rpm. Estimate the total power required (including the power required for the no load situation).

There is now a new generation of mobile crushing and screening plant systems, which have been developed based on the motivation of reducing truck haulage. Newly designed mobile crushing and screening plant systems have the advantages of mobility, flexibility, economy, and reliable performance, making this system very appealing for small- to medium-sized projects or projects where a number of resources are separated by distance. Similarly, the advantages of mobile crushers are lower capital cost (up to 30% less), higher mobility, and higher salvage value at the end of the project life. Mobile crushing plants are not suited to large long-life projects, heavy rainfall climates, or arctic climates. The design considerations, operability, and maintainability require careful consideration. The equipment selection would also be based on different criteria to fixed plant (Connelly, 2013).

The iron ore lump obtained from ROM crushing and screening plants will continue to break down into 6.3mm particles during material handling from the product screen to stockpiles, port, and customer. Drop test conditioning of diamond drill core and crusher lump samples has been developed to simulate material handling and plant stockpiling (Clout et al., 2007). The outcomes of the lump simulations in Figure 2.9 indicate that most of the breakage of lump to 6.3mm fines occurs after the first significant drop height; thereafter, the lump consistently shows the same lower rate of breakage to the extent of testing. Breakage functions can be developed, like the curves in Figure 2.7, for specific iron ores and their hardness categories and then used in subsequent plant engineering design and lump degradation modeling. Different iron ores will show different breakdown characteristics, with very hard iron ores showing a slower rate of breakdown, whereas friable lump breaks down so rapidly that it is unlikely to be economically viable as a lump product (e.g., Figure 2.9, ROM 15 Friable).

Figure 2.9. Simulation of lump yield with cumulative mechanical breakdown in material handling from crusher to port. Lump yield for various hardness types derived from crushing and screening of run-of-mine (ROM) feed.

Large volumes of concrete derived from reliable consistent sources can be regarded as virtual quarries where a mobile crushing plant is used at the site. Examples include RCA derived from the decommissioning of concrete pavements from redundant military airfields or demolition of large concrete framed buildings/industrial facilities.22 In such cases, the availability of a material of consistent quality in large quantities makes their exploitation attractive.

In the UK, there are a growing number of processing centres which combine conventional aggregate processing equipment (such as crushers and screens), with a washing plant. Such facilities have the ability to handle mixed construction demolition and excavation waste (including soil). For commercial reasons, the main output is generally a range of RA products (such as unbound fills, capping, sub-base and pipe bedding) rather than a segregated RCA.15

Annually 1 million tons of mineral demolition wastes mainly consisting of concrete and bricks, is produced in Finland. The crushed materials have in field studies on test roads showed favourable geotechnical properties for use in road constructions. The test samples from two crushing plants were chemically characterised and the leaching behaviour was studied by using column, two-stage batch leaching and pH static tests. Only sulphate and chromium leaching from the crushed material was detected. There was a good agreement between column and batch leaching tests. The contents of harmful organic compounds were very low. Based on experience and the results of the experimental study, a practical sampling and testing strategy for an environmental quality assessment system was developed. A two-stage batch leaching test was chosen for the quality control of demolition waste. Preliminary target values for leaching of sulphate, Cr, Cd, Cu and Pb were set. Both geotechnical and environmental properties of the crushed material indicate that the use of demolition waste in road constructions is acceptable and can be recommended to replace landfilling of this material. However, a detailed demolition plan is most important in order to have an acceptable material for utilisation in earth constructions.

Building garbage recycling equipment in Western developed countries is generally mobile crushing station and mobile screen station, which can be divided into two categories, i.e., wheeled and tracked, shown in Figs 8.5 and 8.6. They can be used either alone or in combination with multiple devices. Characteristics of rubber-tired mobile crushing plant are as follows:

the installation form of integrated complete sets of equipment eliminates complex installation work caused by site and infrastructure of fission components, thus cutting down the consumption of the material and working hours.

The machine adopts all-wheel drive and it can realize spin insitu. Standard configuration and quick change device with perfect function of security protection is especially suitable for narrow space and complex area.

Compared with the traditional crushing screening equipment, the mobile crushing station has characteristics of mobility, reconfigurability, and automation. The crushing, screening, and debris sorting of construction waste can be realized if these features are applied to the recycling of construction waste, which can completely meet the requirements of comprehensive treatment of construction waste. In addition, the combination of different types of mobile crushing station screened by the mobile screen substation, which manage the primary and secondary crushing of construction waste, cannot only improve the performance of recycled aggregates, but also get the recycled aggregates piled up in accordance with the aggregate graded, facilitating the recycle of recycled aggregates.

In the process of construction waste treatment with mobile crushing station, the interaction of the waste concrete with itself contains a mix of collision and friction with each other using vibrating equipment, such as vibrating feeder and the original vibrating screen, which can reduce relatively loose waste mortar on its surface. Compared with the mechanical rub method, there is an effect gap between the two, but it plays the same role as well, which improves the performance of the recycled aggregates to some extent.

New renewable equipment can not only break, but also sieve. Mobile crushing screening equipment produced by Atlas Copco, take PC1375 type I crusher, for example, its high efficiency and flexibility, simplicity of operation, product design for easier transportation make it very suitable for field use in harsh environment, and most important of all, products broken by this device is of high capacity and good quality. PC1375 type I crusher is equipped with a special design of 19-mm-thick conveyor belt with high-strength steel wire, which effectively prolongs its service life. Its standard configuration is high-intensity magnetic belt, which can separate all the metal materials out before conveying crushing material to the dump, producing clean broken end products and the separated metal materials can earn extra income. The discharging mouth of the crusher is equipped with rollers, the impact absorption plate with special design is composed of replaceable rubber and steel, and the conveyor belt is removable, which makes obstruction cleaning and equipment maintenance very convenient.

There are, however, an increasing number of urban buildings built using contemporary earth walling, particularly in Western Australia where the revival of rammed earth as a modern building medium has been particularly prolific.

Alan Brooks, an SRE contractor based in Perth says almost 90% of his current work is urban. He sources limestone rubble and recycled concrete from crushing plants often within the city itself so they can rely on quick deliveries of materials eliminating the need for stockpiling on small sites. Urban SRE is now their main business and they have developed tricks to streamline their production and keep costs down. In other parts of Australia this trend toward more urban earth wall construction is also growing.

Scott Kinsmore is a rammed earth contractor in Melbourne. He says he is building higher walls on smaller urban sites. The engineering for higher walls with more point-specific loads on small-site buildings is challenging and often requires more steel to be built within the wall structures. This can be frustrating and costly for the wall builder. Increasingly, Australian urban architects are meeting the challenges of sensible passive solar design and low embodied energy materials. While much of the current computer modelling that drives our 5 Star Energy Rating programmes is insulation-centric, some designers are using earth walling as a way to limit the embodied energy of their buildings as well as increasing their passive solar capacity.

Particles of sizes in the range of 1400m can be defined as dusts, with particles larger than 100m in size settling down near the source of formation. The total size range can be divided into three classes larger than 20m, 201m, and less than 1m these can be termed as large particles, fines and ultrafines, respectively (Leonard, 1979). The size distribution of dust generated in a crushing plant is indicated in Fig. 12.1. It should be noted that it is more difficult to separate smaller particles from the air stream as they have a greater tendency to remain in suspension (Kumar, 1987).

The amount of dust generated depends upon the type of handling and transportation equipment used. A sensitive location of dust control is generally at the conveyor transfer points, screens, crushers, bins, silos and loading and unloading points (Leonard, 1979). The dust control problem is usually restricted to dry handling of coal preparation plants.

Respirable dust is generally defined as particulate matter less than 10m in diameter according to the US Environmental Protection Agency (EPA). Respirable dust can get into the lungs of human beings and cause pneumoconiosis on prolonged exposure. The quality of air must be maintained so that the concentration of respirable dust does not exceed 2mg/m3. If the quartz content of an air sample exceeds 5%, the average concentration of respirable dust should be less than 2mg/m3 (Meyers, 1981).

The necessity for storage arises from the fact that different parts of the operation of mining and milling are performed at different rates, some being intermittent and others continuous, some being subject to frequent interruption for repair and others being essentially batch processes. Thus, unless reservoirs for material are provided between the different steps, the whole operation is rendered spasmodic and, consequently, uneconomical. Ore storage is a continuous operation that runs 24h a day and 7 days a week. The type and location of the material storage depends primarily on the feeding system. The ore storage facility is also used for blending different ore grades from various sources.

For various reasons, at most mines, ore is hoisted for only a part of each day. On the other hand, grinding and concentration circuits are most efficient when running continuously. Mine operations are more subject to unexpected interruption than mill operations, and coarse-crushing machines are more subject to clogging and breakage than fine crushers, grinding mills, and concentration equipment. Consequently, both the mine and the coarse-ore plant should have a greater hourly capacity than the fine crushing and grinding plants, and storage reservoirs should be provided between them. Ordinary mine shutdowns, expected or unexpected, will not generally exceed a 24h duration, and ordinary coarse-crushing plant repairs can be made within an equal period if a good supply of spare parts is kept on hand. Therefore, if a 24h supply of ore that has passed the coarse-crushing plant is kept in reserve ahead of the mill proper, the mill can be kept running independent of shutdowns of less than a 24h duration in the mine and coarse-crushing plant. It is wise to provide for a similar mill shutdown and, in order to do this, the reservoir between coarse-crushing plant and mill must contain at all times unfilled space capable of holding a days tonnage from the mine. This is not economically possible, however, with many of the modern very large mills; there is a trend now to design such mills with smaller storage reservoirs, often supplying less than a two-shift supply of ore, the philosophy being that storage does not do anything to the ore, and can, in some cases, has an adverse effect by allowing the ore to oxidize. Unstable sulfides must be treated with minimum delay, the worst case scenario being self-heating with its attendant production and environmental problems (Section 2.6). Wet ore cannot be exposed to extreme cold as it will freeze and become difficult to move.

Storage has the advantage of allowing blending of different ores so as to provide a consistent feed to the mill. Both tripper and shuttle conveyors can be used to blend the material into the storage reservoir. If the units shuttle back and forth along the pile, the materials are layered and mix when reclaimed. If the units form separate piles for each quality of ore, a blend can be achieved by combining the flow from selected feeders onto a reclaim conveyor.

Depending on the nature of the material treated, storage is accomplished in stockpiles, bins, or tanks. Stockpiles are often used to store coarse ore of low value outdoors. In designing stockpiles, it is merely necessary to know the angle of repose of the ore, the volume occupied by the broken ore, and the tonnage. The stockpile must be safe and stable with respect to thermal conductivity, geomechanics, drainage, dust, and any radiation emission. The shape of a stockpile can be conical or elongated. The conical shape provides the greatest capacity per unit area, thus reduces the plant footprint. Material blending from a stockpile can be achieved with any shape but the most effective blending can be achieved with elongated shape.

Although material can be reclaimed from stockpiles by front-end loaders or by bucket-wheel reclaimers, the most economical method is by the reclaim tunnel system, since it requires a minimum of manpower to operate (Dietiker, 1980). It is especially suited for blending by feeding from any combination of openings. Conical stockpiles can be reclaimed by a tunnel running through the center, with one or more feed openings discharging via gates, or feeders, onto the reclaim belt. Chain scraper reclaimers are the alternate device used, especially for the conical stock pile. The amount of reclaimable material, or the live storage, is about 2025% of the total (Figure 2.11). Elongated stockpiles are reclaimed in a similar manner, the live storage being 3035% of the total (Figure 2.12).

For continuous feeding of crushed ore to the grinding section, feed bins are used for transfer of the coarse material from belts and rail and road trucks. They are made of wood, concrete, or steel. They must be easy to fill and must allow a steady fall of the ore through to the discharge gates with no hanging up of material or opportunity for it to segregate into coarse and fine fractions. The discharge must be adequate and drawn from several alternative points if the bin is large. Flat-bottom bins cannot be emptied completely and retain a substantial tonnage of dead rock. This, however, provides a cushion to protect the bottom from wear, and such bins are easy to construct. This type of bin, however, should not be used with easily oxidized ore, which might age dangerously and mix with the fresh ore supply. Bins with sloping bottoms are better in such cases.

Pulp storage on a large scale is not as easy as dry ore storage. Conditioning tanks are used for storing suspensions of fine particles to provide time for chemical reactions to proceed. These tanks must be agitated continuously, not only to provide mixing but also to prevent settlement and choking up. Surge tanks are placed in the pulp flow-line when it is necessary to smooth out small operating variations of feed rate. Their content can be agitated by stirring, by blowing in air, or by circulation through a pump.

Recycled concrete aggregate (RCA) comes from demolition of Portland cement concrete. Given that the original concrete might have been strong or weak, dense or open graded, fresh or weathered, then the aggregates pieces can be expected to vary similarly. If the RCA comes from a central recycling plant the consistency will have been addressed, to some extent, by blending of materials from different sources. If the material is coming from an on-site crushing plant then it will reflect more directly, and more immediately, the type of concrete being crushed.

The crushing process produces agglomerations of the original concretes aggregates with adhered mortar. These agglomerations are, typically, more angular than conventional aggregates. Also the crushed concrete will produce fines from the mortar element, the amount being controlled to a large extent by the strength of the original concrete. Thus high-strength concrete will typically crush to produce very sharp, even lance-like, blade aggregates with low proportions of fines, whereas the weakest concrete may crush to produce almost the original coarse aggregates plus a large proportion of fines made of the old mortar. In the crushed mortar component, be newly exposed. The effect of this will be a slow strength gain as this cement starts hydrating either with water that has been deliberately added, or with water attracted hygroscopically from the surrounding environment. Thus RCA is, to some degree, a self-cementing material with RCA from strong concretes (those with high cement contents in the original mix) often exhibiting a higher self-cementing ability.