Aging silo design and equipment selection

By Qing Chenfeng, from ‘Bricks & Tile 2013’

1.Introduction

Under the promotion of national industrial policies such as wall material innovation, building energy conservation, and protection of arable land, the raw materials for brick making have shifted from a single clay to a direction of comprehensive resource utilization: shale, river silt, coal gangue, fly ash, various industrial waste, and construction waste. These comprehensive raw materials have increasingly become the main raw materials for brick and tile products.

At the same time, various product standards in the brick and tile industry are constantly improving, greatly improving the quality requirements of brick and tile products. Enterprises have standards to follow in production, and must also accept supervision and inspection of the quality of relevant national wall material products. Quality standards are increasingly valued in the industry. In addition, the industry has shown an irreversible trend of decreasing the total number of manufacturers and increasing the proportion of manufacturers above designated size. Therefore, the brick and tile industry is facing an increasingly complex nature of raw materials, higher quality requirements, and an inevitable stage of elimination, shuffling, and integration. How to face and grasp this stage has become a strategic consideration that industry insiders and industry elites must face.

1. Overview of brick and tile production process

The production of bricks and tiles mainly involves four major processes: crushing, aging, forming, and firing. For a long time, people have often placed the most emphasis on the forming and firing processes, which cannot be said to be incorrect during certain historical periods. However, with the increasing complexity of raw materials allowed and advocated by the state, the handling of raw materials has become a crucial link. The selection and processing of raw materials directly affect the efficiency, failure rate, and molding quality of subsequent molding equipment. Of course, it also directly affects whether the quality of fired products meets the relevant national quality standards for wall materials. The aging process has an increasingly prominent impact on the physical and chemical properties of raw materials. Aging can not only improve the forming performance of raw materials, but also improve the drying performance of raw materials and improve the quality of products. After 3 days to 6days aging of coal gangue raw materials, the drying waste rate of products can be reduced by 12%, the roasting waste rate can be reduced by 6%, and the plasticity index can generally be increased by 1.5-3. The aging raw material grade has a significant impact on the material performance. Table 1 shows a set of data obtained through experiments:

Table 1: Raw materials properties after aging

Grading ratio（% Mass）		Plasticity Number	Drying sensitivity	Drying linear shrinkage rate %
0.5mm	0.9mm
10	90	5	0.47	1.94
20	80	5.9	0.68	2.06
30	70	6.2	0.66	2.12
40	60	6.3	0.76	2.32
50	50	6.4	0.87	2.34
60	40	7.2	0.85	2.66

From this, it can be seen that the same raw material has different plasticity, drying sensitivity, and linear shrinkage when different particle sizes are used. After forming, the green brick body is uneven, which will cause a large amount of waste loss during the drying and roasting process. Therefore, it is crucial to adopt a reasonable material extraction method after aging to ensure the optimal grading of the raw materials as much as possible. It can be seen that the quality of aging effect and the rationality of material grading directly affect the key indicators of enterprise efficiency such as energy consumption, equipment loss, finished product quality, and qualification rate.

3 Aging silo and aging equipment selection

3.1 Factors affecting the aging silo design

3.1.1 Raw materials

The main raw materials of brick and tile factories include coal gangue, sludge, construction waste, shale, etc., each with its own characteristics, and even the same raw material can have significant differences in performance due to different regions. Therefore, before selecting an aging warehouse, it is necessary to first test the performance of one's main raw materials and draw scientific and realistic conclusions on the performance of raw materials, To determine the necessary aging time to achieve the goal of "raw material aging modification". Currently, the shortest aging time is generally 72 hours, otherwise the aging effect cannot be achieved.

3.1.2 Local climate conditions

China has a vast territory and diverse climate distribution, and in the process of global warming, extreme weather has increased. Every season, there are always some meteorological values that break historical records. According to relevant data, for example, according to the monitoring of summer precipitation and temperature released by the Jiangsu Climate Center in 2011, it rained for over 50 days on June 7th and August. According to the statistics of the Jinhua Meteorological Bureau in Zhejiang Province, as of March 15, 2012, the number of rainfall days was 55 days, with 22 days in January, 23 days in February, and 10 days in March. If a company located in such an area fails to fully consider the impact of the rainy season, considering a daily production of 300000 ordinary bricks, it will produce 1500 fewer ordinary bricks after 50 days of rain. Therefore, the selection of the aging warehouse must take into account the local climate conditions.

3.1.3 Capacity

The design capacity demand must be comprehensively considered in conjunction with the original performance of raw materials and local climate conditions. For example, according to the design production capacity requirement of 300000 ordinary bricks per day, the raw materials can be aged for 3 days to meet the aging requirements, and there is no need to consider the impact of the rainy season. Therefore, the storage capacity requirement for the aging warehouse is calculated as: 300000 ordinary bricks ÷ 430 ordinary bricks/m³ X4d=2790m³。 That is to say, the storage capacity of the aging warehouse must not be less than 2790m³ to meet the production capacity demand of 300,000 ordinary bricks per day. Thus, the design layout of the aging warehouse is determined based on the production capacity demand and capacity.

3.1.4 Match with the selected aging equipment

After considering the above factors, it is essential to determine the specifications and models of the aging equipment. For example, for a rotary side multi bucket excavator, it is necessary to clarify the arm length specifications of the multi bucket excavator, and then determine the design width, height, and excavation depth of the aging workshop based on the arm length specifications.

Because the width, height, excavation depth, and arm length of the aging workshop jointly determine the storage capacity per meter of the aging workshop, any mismatch of these four elements will lead to the expected failure of the other three elements in design, resulting in invalid investment. For example, when the height of the aging workshop cannot meet the requirements, even if the workshop is wider and the multi bucket excavator arm is longer, it will not increase its effective storage capacity.

3.2 Selection elements of aging equipment

The aging equipment mainly refers to the distribute equipment and the material excavator equipment, and this focus is on analyzing the material excavator equipment. The reclaiming equipment mainly includes loaders and multi bucket excavators. How to choose between using a loader or a multi bucket excavator?

3.2.1 Economic comparison

According to the calculation of an annual production of 60 million ordinary bricks, the economic comparison between selecting a loader and a multi bucket excavator with an effective working day of 300 days and a daily working time of 10 hours is shown in Table 2.

Table 2 Loader and Multi bucket excavator economic comparison

Equipment	Power consumption	Unit price	Working time	Daily cost	Annual cost
30 Loader	13 L/H	8 CNY/L	10H	1,040 CNY	312,000 CNY
50 Loader	16 L/H	8 CNY/L	10H	1,280 CNY	384,000 CNY
Multi bucket excavator	10 L/H	0.9 CNY/KW	10H	90 CNY	27,000 CNY

From Table 2, it can be seen that choosing a multi bucket excavator can save costs of around 300,000 yuan per year, which means choosing a multi bucket excavator will earn more profits each year. The original investment situation is that the multi bucket excavator is generally around 150,000 yuan, and the loader is generally around 200,000 to 300,000 yuan.

3.2.2 Grade ratio performance comparison

The previous analysis showed that the particle size distribution of materials has a significant impact on plasticity, drying sensitivity, and linear shrinkage, while the material selection method directly affects particle size distribution. When using a loader to pick up material, it is taken from the bottom of the pile, often with large particles being concentrated. When using a multi bucket excavator to collect materials, the material is collected from different parts of the pile, achieving horizontal and vertical laying, and the particle grading is relatively more reasonable. It can greatly improve the quality of bricks, and the subsequent energy consumption is relatively low.

3.3 The selection factors of multi bucket excavators

Based on the above analysis, it is evident that the multi bucket excavator has obvious advantages in the material collection equipment of aging warehouse. Combining the storage capacity requirements, site requirements, infrastructure costs, design work hours, and other factors of aging warehouse, selecting the appropriate type of multi bucket excavator has a significant impact on the economic benefits of the enterprise.

3.3.1 Advantages and disadvantages of various models of multi bucket excavators

The advantage of side mounted multi bucket excavators is that the equipment has a low one-time investment and an hourly loading capacity of 40m³- 60m³。 The limitation is that about one-third of the area of the aging warehouse needs to be used for the walking track of multi bucket excavators, and the accumulation of aging materials is triangular. That is to say, nearly one-third of the building area of the aging warehouse is used for track laying rather than material storage. Due to the conical shape of material accumulation, nearly two-thirds of the space cannot be fully used for material storage.

The half bridge multi bucket excavator effectively saves 1/3 of the area used for walking tracks, increasing the storage capacity under the same building area conditions, but the accumulation of aged materials is still triangular. The stacking method of triangles is equivalent to a space utilization rate of only 30%. The hourly loading capacity is basically equivalent to the capacity of a side mounted multi bucket excavator.

The bridge type multi bucket excavator not only effectively saves 1/3 of the walking track area of the aging warehouse, but also accumulates the aging materials in the pool in a rectangular shape, fully and effectively utilizing the building space; The bridge type multi bucket excavator can load up to 120m³of material per hour.  This is currently the most advanced and effective aging method in the world. But relatively speaking, the investment in disposable equipment is higher.

3.3.2 How to choose between side type, bridge type or half bridge type multi bucket excavators?

The general concept is to choose a side type for an annual production of 60 million to 100 million blocks, to choose a bridge type multi bucket for an annual production of over 100 million blocks; and to choose a half bridge type for the renovation of old factories subject to site limitation. But what is more valuable is that by considering the design capacity of the aging warehouse comprehensively, the best solution with economic advantages can be determined. Table 3 shows the infrastructure economy comparison between bridge type and side type excavators, for the annual production of 150 million ordinary bricks and the required aging warehouse is 8000m³.

Table 3 Infrastructure economy comparison between bridge type aging warehouse and side type aging warehouse.

（required volume 8000m³, annual capacity 150 million normal bricks）

S/N	Items	Aging Warehouse with Bridge Type Multi Bucket Excavator	Aging Warehouse with Side Type Multi Bucket Excavator	Remarks
1	Civil construction cost	Workshop:86m*20m*10m,Area:1760, Cost: 1760*700=1,232,000 Yuan	Workshop:86*36*10m, Area:3096㎡Cost: 3096*700=2,167,200Yuan	Unit price:700 Yuan/㎡
2	Feeding capacity	Single equipment loading 120m³ per hour, Can meet the annual production of 150 million ordinary bricks	Two equipment loading 110m³per hour, Can meet the annual production of 150 million ordinary bricks
3	Efficient Volume	8400m³	7700m³
4	Distribution direction	Two directions distribution, better homogenization	One direction distribution
5	Total cost of Infrastructure	1,232,000 Yuan	2,167,200Yuan

From Table 3, it can be seen that when meeting the annual production capacity demand of 150 million ordinary bricks, the same storage capacity requirement results in a difference of 935,200 yuan in infrastructure costs due to different selection of aging equipment. At the same time, it can involve using more or less 1,336 square meters of space. Therefore, after determining the design capacity and aging storage capacity, when selecting multi bucket equipment, it is necessary to consider comprehensively the infrastructure cost, as well as various factors such as land cost, local climate conditions, and raw material foundation characteristics. Finally, based on the local situation, the actual conditions and investment scale of the enterprise, the economic optimal decision should be made.