**4. Results and discussion**

The model of choice was the Helical Heat Exchanger. In order to enhance mobility and temperature monitoring, wheels and a thermometer also included in the frame as shown in **Figure 6**. In this model electrical energy is used to melt the plastic making use of an oxygen scavenger to remove oxygen from the reactor. In order to optimize the intended operation, the heat exchanger's dimension was to be calculated. Using Eq. (1) below to calculate the required length of wire, ten turns of the helical copper pipe were chosen.

$$L = N\sqrt{\left(2\pi r\right)^2 + p^2} \tag{1}$$

$$\mathbf{L} = \mathbf{1} \mathbf{0} \sqrt{2\pi \left(7.5\right)^2 + 2\mathbf{0}^2}$$

Using Eq. (2), the helical pipe volume was found.

*Ve*

$$
\overline{V}\_{\epsilon} = \frac{\pi}{4} \left(d\_{\circ}\right)^{2} L
\tag{2}
$$

$$
= \frac{\pi}{4} \left(15\right)^{2} \times 512 = 90.4 \text{ / mm}^{3}
$$

### **Figure 6.**

*SolidWorks model of the heat exchanger (a) assembled heat exchanger (b) exploded view (c) parts list.*

### **4.1 Flexible pavements and bricks experimental results**

The pulverized PET was melted in the pyrolysis chamber in the absence of oxygen Different amounts of PET were used in the mixture with bituminous asphaltic concrete to optimize the best properties from the materials. After testing the compressive strength of the bricks at different percentages of PET the results in **Figure 7** were obtained.

**Figure 7** shows that the compressive strength of flexible pavements decreased with increase in the percentage of the PET. The results showed a maximum

**Figure 7.** *Compressive strength results.*

### *Conceptualization and Design of a Small Pyrolysis Plant for the Sustainable Production… DOI: http://dx.doi.org/10.5772/intechopen.100053*

compressive strength of 10 N/mm2 . However, the water absorption properties decreased with increase in percentage content of PET that is the brick absorbed less water with an increase in the amount of PET.

Since coarse aggregates account for more than 60% of the aggregates, the BAC can be defined as coarse dense-graded and it is suited for all pavement layers and traffic conditions. The PET reduced the flexible pavement and brick compressive strength whilst increasing its fatigue resistance. In addition, it created better mixing between asphalt and the aggregates. During the compressive test the PET bricks had a maximum compressive strength of 10 N/mm<sup>2</sup> which was within the standard range and had less water absorbing tendencies and hence a longer lifespan. Generally bigger aggregate sizes give better mechanical properties, as well as good permeability and traction, and are typically focused at achieving high surface drainage and durability [9]. The flexible pavements with PET as a filler also exhibited increased workability and durability, as well as resistance to irreversible deformation, stress, and low-temperature cracking, and moisture damage [8]. The filler's purpose was to improve stiffness, workability, moisture resistance, and aging properties. The use of waste PET as a flexible pavement is one of the possible uses of the plastic waste.

Globally there is growing demand for high-performance pavement due to increase in traffic and failure of ordinary pavements. In a bid to increase durability of roads especially in developing countries where the roads are deplorable, use of PET waste with BAC and cement as a binder. PET wastes in flexible pavement, brick construction and road rehabilitations would essentially utilize several million metric tons of PET wastes from the waste stream which would have good sustainable effects on the environment such as minimization of pollution and greenhouse gas emissions. It also encourages ecosystem balance by the limiting of non-biodegradable PET wastes from the ecosystem.
