Keywords

1 Introduction

Dust pollution is the main cause of high incidence of occupational diseases such as pneumoconiosis and silicosis among workers, and is also the primary air pollutant in most cities in China. With the increasing efforts of the country in environmental protection and stricter control of occupational diseases among workers, the cost of using dust removal products in factories is also accounting for a higher proportion of production costs. Whether to control and reduce the cost of using and maintaining dust removal products has become a key factor for factories to choose dust removal products.

The traditional dust removal methods mainly include gravity dust removal, filtration dust removal, wet dust removal, and electrostatic dust removal. By comparing and analyzing the market share, dust removal efficiency, dust removal efficiency, preliminary procurement costs, energy consumption costs, and maintenance costs of the three traditional dust removal methods, namely bag filter, inertial dust removal, and spray tower, which have the highest market share, it can be concluded that low-cost equipment has poor dust removal efficiency, while equipment with good dust removal efficiency has higher procurement and maintenance costs [1], as shown in Table 1.

Table 1. Comparison table of traditional dust removal equipment.
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Emerging dust removal methods include photovoltaic dust removal, solar thermal dust removal, etc. The haze removal tower in Xi’an, China, with a height of 60 m and an inner diameter of 10 m, utilizes solar energy to provide heat and drive air circulation, with a haze removal area of 10 km2; at the FedEx in Denver, Colorado, USA, due to the need for a large number of trucks to pass by during work and the high dust emissions, a perforated solar wall panel was installed on the south exterior wall of the factory building, which can provide 76000 m3/h fresh preheated air, saving approximately $12000 annually [2], as shown in Fig. 1.

Fig. 1.
figure 1

Haze removal tower and solar collector wall.

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2 TRIZ Problem Analysis Model

The TRIZ theory uses innovation laws to reveal the general laws and basic principles of the process of creation and invention, mainly to clarify and emphasize the contradictions in the system, with the ultimate goal of completely solving the contradictions in the system and obtaining the final ideal solution [3]. After years of development and dissemination, TRIZ theory has been widely applied in various industries and has long been used as a systematic, knowledge-based, and people-oriented method to solve invention and creation problems [4].

2.1 Current Technical Issues

No matter which traditional dust removal method is used, it is necessary to use electricity to drive the equipment to operate, achieve the effect of air circulation and filtration dust removal, which inevitably requires small and medium-sized enterprises to invest a large amount of electricity bills for dust removal in the factory. In addition, although traditional dust removal equipment has been improved, the problem of occupying a large area remains unresolved.

2.2 Functional Analysis

Firstly, it is necessary to summarize which components a technical system is composed of, including system objects, technical system components, subsystem components, and metasystem components that interact with system components [5]. The functional model obtained by analyzing the interaction relationship between various components of the device is shown in Fig. 2. From the figure, it can be seen that the current system has the following problems:

  1. (1)

    The operation of the equipment can meet the dust removal needs of the factory and ensure the health of workers. However, due to high electricity consumption during use, it can lead to an increase in electricity costs.

  2. (2)

    Each part of the equipment requires shell support, and to ensure sufficient air circulation and flow, it needs to occupy a large workshop space, sometimes even affecting the lighting and ventilation needs of the factory.

  3. (3)

    The accumulation of dust on the bag of a bag filter can lead to a decrease in dust removal efficiency; For factories, the replacement of filter bags is also a significant expense.

Fig. 2.
figure 2

Functional analysis model diagram of traditional bag filter.

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2.3 Causal Analysis

Causal analysis is a method of studying the relationship between the results of the development of things and the causes of their occurrence, and analyzing the factors that affect the causal relationship [6]. Firstly, identify the factors that make the use and maintenance costs of traditional dust removal equipment high, and further evaluate the likelihood of these reasons occurring, using V (very likely), S (some possible), and N (unlikely) as indicators. Evaluate the possibility of solving the reasons marked with V and S, and use three types to indicate them: V (very easy to solve), S (relatively easy to solve), and N (not very easy to solve). Further evaluate the difficulty of implementing corrective measures for reasons marked with VV, VS, SV, and SS, using V (very easy to verify), S (relatively easy to verify), and N (not very easy to verify) as indicators. Draw the above analysis into a causal analysis fishbone diagram [7] (Fig. 3), and from the fishbone diagram, it can be seen that:

Fig. 3.
figure 3

Causal axis analysis diagram.

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3 Apply TRIZ Tool to Solve Problems

In the TRIZ tool, in order to facilitate the definition of contradictions, Archishuler analyzed a large number of patents and successively summarized and extracted 39 general engineering parameters [8]. Using these parameters is sufficient to describe the vast majority of contradictions that appear in the engineering field. Through functional analysis and causal analysis, it has been found that there are three contradictions that make traditional dust removal equipment expensive to use, expensive to maintain, and large in terms of floor space:

  1. (1)

    The contradiction between power and power.

  2. (2)

    The contradiction between shape and force.

  3. (3)

    The contradiction between shape and temperature.

3.1 Physical Contradiction Method

Among the three sets of contradictions, the contradiction between power and power belongs to the physical contradiction [9]. The contradiction between power and power is mainly reflected in the need for dust removal equipment to meet the requirements of dust removal function and dust removal efficiency. It is necessary to use energy to drive air circulation and flow, allowing dusty air to enter the interior of the dust removal equipment and achieve dust removal function. However, the consumption of electrical energy is the main reason for the high cost of use. Simply put, this contradiction is: equipment cannot run without electricity, and electricity is expensive.

In response to this contradiction, the “conditional separation” method among the four separation methods of TRIZ is adopted to separate the electrical energy, change the energy supply, and achieve the purpose of dust removal.

3.2 Technical Contradiction Method

Among the three sets of contradictions, the contradiction between shape and force, and the contradiction between shape and temperature belong to technical contradictions [10]. Among the 39 general parameters, the 12th parameter “shape” is an improvement parameter. We can improve the performance of the product through shape, such as reducing volume to reduce land occupation; The 10th parameter “force” and the 17th parameter “temperature” are deterioration parameters. Due to changes in shape, it may lead to a decrease in the power of air flow required for dust removal and a change in air circulation temperature, greatly affecting dust removal efficiency. Find the parameter No.12 shape that the system needs to improve in the first column of the contradiction matrix, find the deteriorating parameter No.10 force and No.17 temperature in the first row, and find the corresponding invention principle, as shown in Fig. 4.

Fig. 4.
figure 4

Using Contradiction Matrix to Derive Invention Principle Diagram.

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  1. (1)

    According to Article 22 of the Invention Principle, the principle of turning harm into profit is to replace the equipment structure that originally occupied a large area of the factory area with a wall. The wall itself is a necessary enclosure structure for the factory building, and replacing the equipment with it can greatly reduce the land occupied due to dust removal needs.

  2. (2)

    According to Article 32 of the Invention Principle, the principle of color change, the efficiency of coating solar thermal conversion is the source of aerodynamic force, and the higher the conversion efficiency, the greater the power obtained by the air.

  3. (3)

    According to Article 37 of the Invention Principle, the principle of thermal expansion, we simulate and adjust the size of the wall through software to obtain the optimal wall height to thickness ratio. The air inside the wall can be fully heated by solar thermal energy, maximizing the power of air circulation.

  4. (4)

    According to Article 40 of the Invention Principle, the principle of composite materials, a new sandwich composite wall is formed by combining solar photovoltaic panels with the wall.

3.3 Material Field Analysis

Although photovoltaic power supply can solve the problem of high electricity bills for traditional dust removal equipment, there are still the following problems:

  1. (1)

    Susceptible to dust pollution, long-term use of surface ash affects photoelectric conversion efficiency.

  2. (2)

    Each square meter of photovoltaic panels costs about 900 RMB, and it is not a small cost to use them on a large area outside the factory building.

  3. (3)

    During long-term use, the voltage board may face surface damage and require investment in replacement.

In response to the most serious issue of photoelectric conversion efficiency in the product, the TRIZ method was used to analyze the material field of the product, and solution 6 was used. Firstly, it was determined that the low photoelectric conversion efficiency was insufficient. Therefore, we searched for solutions in the second and third standard solutions. The final selection number 2.2.1, the 16th standard solution, is to replace the previously difficult to control field with a field that is easier to control, or to superimpose it on the field that is not easy to control. Using “solar thermal conversion” as a “more easily controllable field”, solar energy is directly converted into thermal energy. By utilizing the chimney principle of hot air rising and cold air falling, solar energy directly drives air circulation.

4 Scheme Description

By continuously developing and iterating with TRIZ tools, we have innovatively invented an air circulation self dust removal prefabricated wall, as shown in Fig. 5.

The wall is composed of three parts: outer wall, middle cavity, and inner wall.

  1. (1)

    The exterior wall is a solar thermal module, composed of organic heat absorbing materials and aluminum based thermal conductive materials developed by us with independent knowledge products. It absorbs solar energy, heats the air in the cavity, and promotes air circulation and exchange.

  2. (2)

    The middle chamber is an air circulation dust removal module that uses high-voltage static electricity to form an electrostatic field to adsorb dust in the air inside the chamber.

  3. (3)

    The inner wall is a thermal insulation module made of recycled building solid waste materials. It utilizes recycled building waste materials, which are lightweight, have a large pore ratio, and have good insulation effects. It plays a role in isolating temperature transmission and ensuring room temperature.

The working principle is shown in Fig. 5: When sunlight shines on the outer side of the factory building, the sunlight is captured by the external wall photothermal module, which heats the external wall and conducts convection and radiation heat exchange with the dust containing air in the dust removal cavity. At this time, the dust containing air in the dust removal cavity is rapidly heated and rises, causing negative pressure at the bottom of the wall, causing the bottom of the inner wall to suck in the dust containing air. The dust in the dust containing air is captured by the electrostatic dust removal device, and the remaining clean air rises along the wall, Finally, it is discharged from the exhaust outlet on the top of the exterior wall.

Fig. 5.
figure 5

Product model and schematic diagram.

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Install the product with a length of 5 m and a height of 2.6 m on the outer side of the factory building with a length of 50 m, a width of 20 m, and a height of 9 m. Under the condition of solar irradiance of about 600 W/m2, conduct a test on the dust removal effect of traditional bag filter and this air circulation self dust removal assembly wall. The experiment has shown that in the first 20 min, the dust removal efficiency of the prefabricated dust removal wall is not as good as that of the traditional bag filter, but after 20 min, the dust removal efficiency is basically the same as that of the bag filter (Fig. 6).

Fig. 6.
figure 6

Dust removal effect test and relationship diagram between indoor dust concentration and dust removal time.

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In addition, the air flow rate and flow rate in the dust removal chamber show an upward trend with the increase of solar radiation intensity. The higher the solar radiation intensity, the more energy is absorbed by the surface of the collector wall, resulting in a greater difference between the hot air density in the dust removal chamber and the air density in the external environment, resulting in a greater suction force that increases the air flow rate in the dust removal chamber. By detecting and analyzing the wind speed at the bottom entrance of the inner wall under different illuminances (Fig. 7), it is found that when the solar irradiance is 600 W/m2 or above, the air flow rate can meet the dust removal requirements.

Fig. 7.
figure 7

Relationship between air inlet wind speed and solar illumination.

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The solar irradiance is the key to ensuring the dust removal effect of the product. However, when the solar irradiance is insufficient on rainy days, it is still necessary to use photovoltaic dust removal walls for assistance. Firstly, solar energy is converted into electrical energy and stored in batteries. When the solar irradiance is insufficient, air circulation power is provided for the dust removal walls. The configuration ratio of the solar thermal dust removal wall and the photovoltaic dust removal wall is adjusted according to the geographical location of the factory building.

In addition, the intensity of solar radiation has a pattern of high in summer and low in winter, and summer is the peak of electricity consumption. For factories, relying solely on industrial electricity for dust removal in their factories will not only greatly increase the cost of electricity, but also make it impossible to use traditional dust removal equipment due to peak electricity usage. However, for solar powered dust removal walls, there is no such problem, as higher solar radiation intensity can provide strong power for air circulation. In summer, the filtered clean air with higher temperature is discharged from the top of the exterior wall, and the thermal insulation inner wall composed of recycled building waste materials can effectively isolate outdoor high temperatures. In this way, the solar dust removal wall not only has dust removal function, but also effectively reduces room temperature. In winter, the filtered clean air with higher temperature returns from the top of the inner wall to the inside of the factory building, playing a heating role.

5 Conclusion

  1. (1)

    Establish a functional model of traditional dust removal products using the functional analysis in TRIZ theory; Using causal analysis fishbone diagram to identify the key issues that lead to high energy consumption and maintenance costs of traditional dust removal equipment.

  2. (2)

    Use technical contradictions, physical contradictions, and contradiction matrices to find the corresponding invention principles to solve the problem, and propose a solution to use solar energy to provide power, replacing the metal shell of traditional dust removal equipment with a wall.

  3. (3)

    Using physical field analysis and the 16th standard solution out of 76 standard solutions, replacing solar photovoltaic panels with solar thermal coatings can solve the problems of low photovoltaic conversion efficiency and maintenance costs.

  4. (4)

    The test on the air circulation self dust removal prefabricated wall shows that when the solar irradiance is 600 W/m2 or above, the product can meet the dust removal needs of small and medium-sized enterprise factories. This provides a foundation for subsequent analysis.

  5. (5)

    Due to the significant impact of weather on the performance of solar thermal dust removal walls, it is still necessary to retain some photovoltaic dust removal walls and use solar energy to provide electricity to drive air circulation.

  6. (6)

    In summer, hot air is discharged from the top of the exterior wall to achieve indoor cooling; In winter, hot air returns from the top of the inner wall to the interior, achieving heating.