Selection and matching of heating equipment in asphalt pavement maintenance

In the maintenance of asphalt pavement, there are various heating technologies and heating equipment available for selection:

I. Commonly Used Heating Technologies

1. Direct flame heating

Direct flame heating should avoid direct contact between the flame and the asphalt mixture as much as possible. The heat mainly relies on conduction and convection to heat the mixture. The distribution of heat inside the equipment is uneven, and there are high-temperature zones. However, the equipment has a simple structure and low cost.

2. Hot air circulation heating

Cold air is heated by a heat source, and the hot air is continuously circulated through a circulation device to heat the asphalt mixture and asphalt pavement. It features high thermal efficiency and easy temperature control, and is widely used in on-site hot regeneration and in-situ hot regeneration.

3. Heating with heat transfer oil

Heat transfer oil is an excellent heat transfer medium. The heat source indirectly heats the caulking material, asphalt or asphalt mixture through the fire tube, heat transfer oil and heat transfer wall. The heat distribution of heat transfer oil is uniform, the temperature is easy to control precisely, and it is conducive to ensuring the road performance of the material after heating.

4. Far-infrared heating

The principle of infrared heating: It utilizes infrared radiators to generate electromagnetic waves. When the frequency of these waves is close to the natural frequency of molecular motion in the heated object, it causes resonance among the molecules in the object, resulting in friction and the generation of thermal energy to achieve the heating purpose. There are two types of heating methods for infrared radiators: direct heating and side heating. In the maintenance of asphalt pavement, side-heating infrared radiators are mainly used. Use the combustion of liquefied gas as a heat source. According to the different materials of the combustion surface, there are two mainstream products: metal fiber infrared radiators and microporous ceramic infrared radiators. It is applied to asphalt heating, asphalt mixture heating and asphalt pavement heating.

5. Microwave heating

Heating principle: Repeatedly polarizing the medium in an alternating electric field causes intense friction between molecules, thereby generating thermal energy. Microwave heating is closely related to the properties of the material being heated. The dielectric constant of the material is the ease with which it is polarized in a magnetic field. Media with high dielectric constants can be easily heated by microwaves.

Microwave heating can improve the problem of asphalt aging during the heating process of asphalt mixture. It generates less harmful substances during heating and is a more environmentally friendly heating method.

Ii. Selection and Matching of Heating Equipment

When selecting and configuring heating equipment, the first step is to determine a reasonable configuration quantity

When the maintenance mileage is determined, either too much or too little heating equipment configuration will have an adverse impact on the maintenance work. Due to the fact that the construction quality of each road, the climatic conditions of the area where it is located, traffic flow and other situations are all different, the number of heating equipment configured should not be a fixed value. Instead, statistical methods should be used for calculation based on specific circumstances.

Some heating equipment has strong seasonality and periodicity during use, resulting in a situation where there is a relative shortage or surplus of equipment during peak and off-peak periods. This can be regulated through methods such as leasing and renting.

2. Compare the costs of the heating equipment

The cost of heating equipment should be comprehensively balanced between the procurement cost and the usage cost to maximize the benefits of the input and output of the heating equipment. Procurement costs are transparent and relatively easy to control through bidding. Usage costs, on the other hand, are implicit and should also be the focus of cost comparison. The following factors are usually taken into consideration:

The market prices of energy sources such as electricity, gas and diesel are different. After being converted into the same amount of thermal energy by different heating devices, there will be A price difference among them. Over time during the use of the equipment, a significant cost difference will accumulate. The price difference of energy should be reasonably estimated based on the specific local conditions.

B) The service life, price, supply cycle, and distribution of maintenance outlets of the heating elements all have a significant impact on the operating cost of the equipment. The manufacturer is required to provide detailed and accurate information for reference.

C) The heating efficiency of different heating equipment varies. Under the same heating area, compare the heat generation of the equipment with the theoretical heat absorption of the asphalt mixture when heated to the required temperature.

=Q1/Q

Q1= Heat output of the heating equipment

Q= Theoretical heat absorption of the mixture =MC(T2 - T1)

The quality of M asphalt mixture

The specific heat of C asphalt mixture

The temperatures of T1 and T2 materials before and after heating

Heating equipment with an η value close to 1 has a high thermal efficiency, saves energy during use and has a low operating cost.

3. Compare the performance of the heating equipment in use

A) Different heating devices have different effects on asphalt mixtures during the heating process. The road performance of the heated mixture should be evaluated through tests.

B) In maintenance projects, environmental protection requirements are getting higher and higher, and some heating equipment with greater pollution will gradually be phased out. The environmental performance of heating equipment should be compared and selected, and its pollution emissions should comply with national standards.

C) When purchasing equipment, it is necessary to consider whether there are any limitations in the application scope of the equipment. For example, infrared heating equipment made of microporous ceramics is not suitable for use in situations with large vibrations and frequent movement due to its high fragility and poor impact resistance.

4. The influence of external factors should be taken into account in the selection and matching process

In addition to the factors of the equipment itself, the selection and matching of equipment should also take into account the influence of external factors such as the maintenance price, the unit's capital flow, and the mandatory terms for equipment types in the maintenance contract.

In conclusion, maintenance units should find suitable heating equipment through comprehensive evaluation to avoid waste of investment.