Waste cooking oil (WCO) Operated Domestic Cook- stove with PRB
6.2 Design and fabrication of WCO/kerosene blend operated PRB
Proper selection of porous matrix is the key factor for achieving better thermal efficiency and lower emissions. In order to study the effect of porous matrix diameter on the thermal efficiency of the burner, series of experiments have been performed (Sharma et al., 2011, 2016a, 2016b). It was found that the burner with 70 mm diameter
yielded the maximum thermal efficiency. Therefore, SiC matrix of 70 mm has been chosen for the present investigations. This work is an extension of the earlier PhD work on the development of pressurize kerosene burner for kerosene stove (Sinha, 2017).
Figure 6.3 shows the schematic of the earlier developed PRB for kerosene application.
Retrofitting the PRB in the commercial pressure kerosene stove leads to the significant improvement in thermal efficiency and reduction in emissions (Sinha, 2017). However, this burner was designed for pure kerosene application. Therefore, for WCO application vaporizer has been modified.
Fig. 6.3: Kerosene operated PRB developed by Sinha, 2017.
With the vaporizer developed by Sinha (2017) only partial red hot surface was noticed in SiC for WCO blend samples. It was because of increase in viscosity of fuel which degraded the spray characteristics. As heating of incoming WCO and kerosene blend before spray nozzle is the only option to improve the combustion characteristics.
Vaporizer developed by Sinha (2017) was unable to recirculate heat to incoming fuel (Fig. 6.4). Reason behind this is the less contact area available between the porous media and burner (vaporizer). Therefore, a new vaporizer was developed with modified design. The modified vaporizer is shown in Figure 6.5.
Fig. 6.4: PRB assisted kerosene vaporizer developed by Sinha, 2017.
Fig. 6.5: Newly developed PRB for WCO and kerosene blend application.
In PRB, four 8 mm diameter copper tubes, two each ascending and descending, connected with a circular tube of 9 mm diameter copper tube (vaporizer) on top and SiC as CZ in mild steel burner casing, act as the burner (Fig. 6.5). Schematic of newly developed PRB is shown in Fig. 6.6. Stoves with PRB consists of a hand pump, fuel tank with integrated pressure gauge and one rising tube. Pressurizing the fuel in tank forces it to move through the rising tube and then to the vaporizer. A regulator is provided to maintain the intended amount of fuel flow rates. Apart from these components, the PRB is provided with a heat shield ring which reduces the heat loss to the surrounding. For comparative performance assessment with CB, BIS specified Roarer stove was used (Fig. 6.7). As shown in Fig. 6.8, the CB consists of two ascending and two descending tubes. These tubes touch the vaporizer (which is a flat circular chamber) and the ascending tubes remain connected with the riser. Middle section of the descending tubes contains the spray nozzle, through which kerosene vapor is sprayed in air. Apart from these components, the CB is provided with a flame holder, which helps in stabilizing the flame.
Fig. 6.6: Schematic of newly developed PRB for WCO and kerosene blend application.
Fig. 6.7: BIS specified Roarer stove.
Fig. 6.8: Details of CB in Roarer stove.
Detailed specifications of the stove, nozzle, CB, and porous insert used in the investigation are provided in Table 6.2.
Table 6.2: Specifications of CB and PRB for WCO and kerosene blend application.
S.
No. Components Specification
1. Fuel tank capacity 3 liter
2. Fuel tank pressure 1.5 bar
3. Fuel used kerosene and WCO blends
4. CB Commercially available burner
5. Nozzle Spray nozzle with 0.454 mm diameter
6. PRB
SiC 70 mm dia., 20 mm thickness, 90%
porosity Perforated
sheet
70 mm dia., 2 mm thickness, 17%
porosity, 1.5 mm hole dia.
Initiation of the combustion process in both burners is quite similar, but the principle of combustion is different. The vaporization process in both burners is initiated when a little quantity of kerosene is burnt in the spirit cup (provided just below the burner).
The liberated heat is transferred to the vaporizer, and vaporized fuel moves down through descending fuel tubes and is ejected from a central nozzle. In CB, fuel vapor from the nozzle burns near the vaporizer and downward heat transfer from the flame sustains further combustion. However, in PRB, the flame is trapped by ceramic material (SiC), and the highly emissive nature of the porous insert promotes the radiative heat transfer in all possible directions, which is insignificant in CB. A clear visible flame near the vaporizer is not seen, rather the ceramic becomes red hot. The PRB is then said to operate in radiative mode. Temperature fluctuations on the burner surface have been observed. Burner operation is considered stable when the fluctuations remain within 10°C for at least 30 min. Schematic of the experimental setup used for thermal efficiency and emission measurements is shown in Figure 6.9. Technical specifications of different instruments used during experiments are given in Table 6.3.
Fig. 6.9: Schematic of the experimental setup for WCO and kerosene blend operated cook-stove.
Table 6.3: Technical specifications of the instruments used in experimental studies.
Instruments Functions Uncertainty
Weighing balance (SES15TH)
Measurement of the weight of the stove, water, Aluminium vessel,
and food items
±1 g Portable flue gas analyzer
(Testo 340)
CO NOx
±2 ppm
±2 ppm
Thermometer Temperature of water ±1°C
Thermocouples & Data
acquisition unit (DAQ) Temperature of burner ±1°C
Pressure gauge Pressure in fuel tank ±1 mbar