Abstract

Diesel-operated vehicles are commonly used by personnel in underground mines. Although these vehicles facilitate travel within the mine, their main disadvantage is that they generate diesel particulate matter (DPM), a known carcinogenic agent. This calls for research to control the spread of DPM in underground mines in order to ensure the safety of mine personnel. In this article, the flow patterns of DPM generated by two types of diesel-operated vehicles are modeled using computational fluid dynamics (CFD) simulations. The simulation results are validated using field experimental measurements. The models show that if the vehicle is stationary, DPM particles are dispersed towards the center of the gallery and occupy the entire cross section of the road way. Vehicle movement induces air currents that may result in the miners being exposed to high DPM concentrations. The results show that if the DPM and the intake air counter-flow (flow in opposite directions), the DPM spread occurs throughout the entire cross-section of the roadway. This research is expected to contribute to the formulation of effective DPM control strategies in underground mines.

Keywords: underground mines, DPM, diesel-powered man riding vehicle

### 1. Introduction

As underground mines go ever deeper and spread over larger areas in an attempt to meet ever-increasing production targets, there is a correspondingly significant increase in the usage of diesel-powered vehicles. Most of the mines in the world have been using diesel-operated vehicles for transportation of men, material, ore, waste rock, coal and for various other mining operations. The commonly used diesel-operated vehicles in underground coal, metal and non-metal mines are trucks, load haul dumpers (LHD), Jumbos, cable bolters, long hole drilling rigs, man-riding vehicles, telehandlers, graders, water tankers, forklifts, articulated wheel loaders, agitators, shotcrete sprayers, etc.

Diesel-powered vehicles offer greater flexibility than electric and batteryoperated vehicles because they can travel over longer distances and between working sections. The use of diesel vehicles is efficient, as evidenced by ease of

maintenance, consistency and durability. Many nations have depended on these vehicles for these reasons [1].

Diesel is a mixture of hydrocarbons. In a perfect diesel engine, oxygen (O2) from the air converts all the hydrogen (H2) in the fuel to H2O and the carbon (C) to CO2, while the nitrogen (N2) in the air remains unaffected. But in the reality, the combustion process is not perfect, and the engine emits several pollutants due to incomplete combustion [2].

$$\text{Fuel} + \text{Air} \rightarrow \text{Unburned hydrocarbons} + \text{NO}\_x + \text{CO}\_2 + \text{CO} + \text{Water} \tag{1}$$

The diesel engine exhaust fumes mainly contain a mixture of diesel particulate matter (DPM) and other pollutant gases such as nitrogen oxides (NOx), hydrocarbons (HC), including either total hydrocarbons (THC) or non-methane hydrocarbons (NMHC) and carbon monoxide (CO) [3].

Different nations recommend different safe occupational exposure limits (OEL). Table 1 shows the OEL used in Australian underground mines.

The ventilation air requirement to dilute any of the gases (CO, CO2, SO2, NO and NO2) or DPM emitted by a diesel engine to the targeted concentration level (Qv) can theoretically be calculated for any given movement using the following equation [2]:

$$\mathrm{Q\_V}[m^3/s] = \frac{\mathrm{Q\_E}[m^3/s] \, X \, (\mathrm{C\_E}\,\mathrm{[ppm\ or\ \mu g/}m^3] - \mathrm{C\_T}\,\mathrm{[ppm\ or\ \mu g/}m^3])}{\mathrm{C\_T}\,\mathrm{[ppm\ or\ \mu g/}m^3] - \mathrm{C\_B}\,\mathrm{[ppm\ or\ \mu g/}m^3]} \tag{2}$$

Where Q<sup>E</sup> is exhaust flow rate, CE is the concentration of the specific pollutant (gas or DPM) in the exhaust, C<sup>T</sup> is target concentration of the corresponding gas or DPM and C<sup>B</sup> is the concentration of the specific pollutant (gas or DPM) in the dilution air.

As per the Australian Mines Regulations and Act [4–6], to minimize exposure of mine personnel to diesel emissions, the mine operator must collect diesel engine


Where,TWA 8 is 8-hour time weighted average and STEL is short term exposure limit.

\*STEL refers to the maximum concentration where personnel can work for a maximum of 15 minutes at a time. A maximum of 1 hour per shift can be allowed provided that it is broken up into four 15-minute work intervals, with a minimum 1-hour break in between work intervals.

\*\*Gases are treated as acute hazards; therefore, reduction factors based on hours worked per shift can be applied to the standard OEL (TWA 8). A 10-hour shift will have a reduction factor of 0.7 and 12-hour shift will have a reduction factor of 0.5 applied to the target gas.

\*\*\*Particles are treated as chronic hazards. The OEL (TWA 8) needs to be adjusted according to the shift roster worked by the work group. Reference can be made to the formula: Reduction factor = 170/x where x is the number of hours worked per month.

#### Table 1.

Workplace exposure limits of diesel vehicle emissions [3].

Analysis of Diesel Particulate Matter Flow Patterns in Different Ventilation and Operational… DOI: http://dx.doi.org/10.5772/intechopen.84651

exhaust samples in underground mines and analyze the samples. The results of the analysis are compared with the baseline exhaust emissions for the diesel engine. All underground diesel engines are regularly maintained so that emissions from the engine are as low as is reasonably practicable with respect to the base line exhaust emissions. The mine operator must also maintain the standard fuel or fuel additive quality and DPM filters.

#### 1.1 DPM

The chemical composition of DPM depends on the compositions of the fuel and the lubricating oil, engine technology, operating conditions, and the technology used to treat the exhaust. The major contributors to the total particle mass emitted by diesel engines include elemental carbon (EC), organic carbon (OC), inorganic ions such as sulfates, nitrates, ammonia, sodium, chloride ions, and trace metallic compounds [2].

EC and OC emissions, cumulatively known as 'total carbon (TC)', make up the largest fraction of aerosols emitted by diesel engines. TC is generally considered to make up about 70–90% of DPM. On an average, elemental carbon comprises 50– 70% of TC and greater than 45% of 'total engine-out' DPM emissions. The engineout organic carbon makes up between 10 and 80% of total carbon [2].

The EC fraction of DPM is a product of the pyrolysis of the fuel and the lubricating oil in the combustion chamber. The OC fraction of exhaust emissions from a diesel engine is a complex mixture of burned and unburned lubricating oil and fuel compounds.

#### 1.2 DPM size distribution

DPM particles are very small and are subdivided into three categories with respect to size: Nano-particles less than 50 nm in diameter, ultra-fine particles less than 100 nm in diameter and fine particles less than 2.5 μm in diameter. Figure 1 shows a typical DPM size distribution weighted by number, surface area, and mass [7].

The DPM is composed of numerous small particles with very little mass, mixed with relatively few larger particles, which contain most of the total mass. A small fraction of diesel particles resides in the third, 'coarse' mode.

Figure 1. DPM particles size distribution [7].

The DPM particles of size ranging from 3 to 500 nm are more dangerous for human health. These particles can get lodged in the alveolar regions of the longs where gas exchange takes place [2].

Various research studies have been conducted to better understand the effects of DPM on human health [1, 8–10]. These studies have concluded that exposure to diesel exhaust may cause cancer in humans.

The effective density of DPM decreases sharply from 1.2 g/cm<sup>3</sup> for 30 nm particles to 0.3 g/cm<sup>3</sup> for 300 nm particles. The effective density of agglomerated diesel particles varies from 1.1 to 1.2 g/cm<sup>3</sup> . The chemical composition of DPM has not been observed to follow any trend and it mainly depends on engine oil and diesel chemical composition [11].

#### 1.3 Workplace exposure limits on DPM in underground mines

Different countries follow different workplace exposure limits and mine ventilation standards to deal with DPM. Table 2 shows a summary of DPM exposure limits and ventilation requirements. The regulations in different countries are outlined in the following sections.


MSHA: Mine Safety and Health Administration.

ACGIH: American Conference of Governmental Industrial Hygienists.

RCD: Respirable Combustible Dust.

CANMET: Canada Centre for Mineral and Energy Technology.

#### Table 2.

International DPM exposer limits and ventilation standards [12].

Analysis of Diesel Particulate Matter Flow Patterns in Different Ventilation and Operational… DOI: http://dx.doi.org/10.5772/intechopen.84651

As per the Australian Coal Mines Work Health and Safety (WHS) Regulations 2006 [6], WHS (mines) Act 2013 [5] and WHS (mines) Regulations 2014 [4], the maximum allowable workplace exposure (mine atmosphere) for DPM in the elemental carbon (EC) form when expelled from a diesel engine is 0.1 mg/m<sup>3</sup> . This is approximately equal to 0.16 mg/m<sup>3</sup> of TC or 0.2 mg/m<sup>3</sup> DP.

As per Australian WHS mines act and regulations, the volume of air in each place where a diesel engine operates must be such that a ventilating current of not less than:


The ventilation air flow is directed along the airway in which the engine operates. If more than one diesel engine is being operated in the same ventilating current, the engine kilowatts must be added, and the minimum ventilation requirement is 0.06 m<sup>3</sup> /s/kW or 3.5 m<sup>3</sup> /s, whichever is greater.

The minimum mine ventilation quantity to dilute diesel particulate exhaust emissions to 0.1 mg/m3 (diesel particulate signature) QDP(min) can be calculated using the following equation [3]:

$$\mathbf{Q\_{DP(min)}} = \frac{\mathbf{EC\_{kW}}}{\mathbf{3600DP\_{(Expour limit)}}} \mathbf{P\_{WA}} \tag{3}$$

where QDP(min) is minimum mine ventilation quantity (m<sup>3</sup> /s), DP(Exposure limit) is 0.1 EC (mg/m3 ), ECkW = sum of weighted average diesel particulate (EC) per hour emitted from the diesel engine exhaust over the specified duty cycle (mg/h) and PWA is sum of weighted average power for the diesel engine over the duty cycle (kW).

#### 1.4 Previous DPM field investigations in underground mines

The National Institute of Occupational Health and Safety (NIOSH) organized a detailed DPM field study on the effectiveness of diesel-vehicle filters and bio-diesel in isolated underground environment at the Nye Mine run by the Stillwater Mining Company [13]. This study was conducted by a partnership formed by NIOSH, the National Mining Association (NMA), the National Stone, Sand and Gravel Association (NSSGA), the United Steel Workers of America (USWA) and the MARG Diesel Coalition [13]. Two trucks and three load haul dumpers (LHDs) were used for this experiment. The main aim of this study was to study the effectiveness of the diesel particulate filter (DPF) systems. In this study, the tested DPF systems were Engelhard DPX, DCL MineX, Clean Air System, DCL Blue Sky, Mac's Mining Repair/Donaldson P604516, ECS Cattrap and Biodiesel [13].

Subsequently, the effectiveness of the DPF systems to control DPM and gases was assessed under the diesel emissions evolution program (DEEP). This study was conducted at an isolated mine zone of Narannda's Brunswick Mine in Bathurst. This study involved the Burnswick mine, Natural Resources Canada, Canada Centre for Mineral and Energy Technology (CANMET), National Institute of Occupational Safety and Health (NIOSH), Andreas Mayer of VERT and DPF systems suppliers [14]. Four 242 kW LHDs and two 278 kW haulage trucks were used for this study. The tested DPF systems were ECS catalyzed filter, ECS octel filter, DCL catalyzed/ electric filter and Oberland Mangold octel filter [14].

Recently, as a part of Ph.D. research, a DPM field study has been conducted at an experimental mine at the Missouri University of Science and Technology. The aim of the research was to study DPM dispersion in underground metal/non-metal mines [15]. A 30 kW Skid-steer loader was used for this study [15].

A greater understanding of DPM flow patterns in different conditions will help control the miners' exposure to the high concentrations of DPM in the vicinity of diesel-operated vehicles. This chapter describes a detailed study of DPM flow patterns generated by diesel-operated man-riding vehicles and LHDs, using field experiments and computational fluid dynamics (CFD) investigations. The field experiments and CFD simulation studies were conducted in two stages: stage 1 with a man-riding vehicle and stage 2 with an LHD, both with different air flow directions.

### 2. Experimental investigation

#### 2.1 The experimental site

Field experiments were conducted in an Indian coal mine, 'mine A', in one of the eight working seams in the mine. The mine has a number of bord and pillar and long wall working sections. The mine uses diesel-operated man-riding vehicles, LHDs and shuttle cars. The ventilation system of the mine consists of five intakes and two return shafts with two main axial flow fans. The operating parameters of the two fans are: air flow of 150 m<sup>3</sup> /s at 510 Pa pressure and air flow of 140 m<sup>3</sup> /s at 400 Pa pressure respectively.

#### 2.2 Details of field experiment 1

A calibrated 'Airtec' real-time DPM monitoring instrument was used for these field experiments. This instrument measures the concentration of elemental carbon (EC) or total carbon (TC) in real time. This instrument works on the principle of laser diode absorption technique [16, 17]. This monitor uses technology developed by the diesel particulate group at the NIOSH Pittsburgh Research Laboratory and has been determined to precisely replicate results from their method 5040 test. This monitor can help prevent safety non-compliances, ensuring increased miner safety [18].

The flow rate and sampling time of the DPM monitor was adjusted to 2.83 <sup>10</sup><sup>5</sup> <sup>m</sup><sup>3</sup> /s (1.7 liters per minute) and 5 minutes respectively. Before the experiment, the location of vehicle, smoke pipe (DPM source), sampling stations were determined and marked on the gallery. During the experiment, the vehicle position was not changed. An average of three 5-minute sample were taken at each sampling station.

Figure 2 shows the locations and arrangements of sampling stations and sampling points (a, b and c). During this experiment, the engine was run under a 'no-load' condition.

To ensure that the intake air was devoid DPM, the experiment was conducted in one of the intake airways near the bottom of the shaft. The length, width and height of the gallery were measured to be 100, 6 and 2.7 m respectively. During the experiment, the intake air velocity was maintained at 1.26 m/s. The velocity and temperature of the vehicle exhaust fumes were measured to be 29 m/s and 323 K respectively.

Analysis of Diesel Particulate Matter Flow Patterns in Different Ventilation and Operational… DOI: http://dx.doi.org/10.5772/intechopen.84651

#### 2.3 Details of field experiment 2

In this experiment, the LHD exhaust smoke was directed opposite to the ventilation air flow. DPM samples were measured downstream side of the LHD. In this case, DPM samples were collected around the LHD and also at 6, 10 and 20 m downstream of the LHD at a height of 1.2 m from the floor. At each sample station, three samples were measured, each over a 5-minute duration. The average of the three readings was considered as representative of that sample station.

Figure 3 shows the location and details of the sampling points. DPM was measured at 11 sampling stations, Figure 3. During this experiment, the air flow in the experimental gallery was 20.4 m<sup>3</sup> /s.

As in field experiment 1, the flow rate and sampling time of the DPM monitor was adjusted to 2.83 <sup>10</sup><sup>5</sup> <sup>m</sup><sup>3</sup> /s (1.7 liters per minute) and 5 minutes respectively. Before the experiment, location of vehicle, smoke pipe, sampling stations were measured and marked on the gallery. During the experiment, the vehicle position was not changed. Average of three 5-minute samples were taken at each sampling station.

Figure 2.

Locations of sampling stations and sampling points w.r.t DPM source (vehicle).

Figure 3. Locations of sampling stations and sampling points, top view.
