Chapter 20: Bulk Trucks
Availability of explosives in bulk form in the 1960s marked the beginning of the large-scale use of bulk trucks. This time marked the first use of water gel explosives capable of being custom manufactured in bulk trucks at the borehole. At this time water gels were considered specialty products and were used primarily at larger mining sites.
The new water gels were the product of an aggressive industry effort to develop products that were less sensitive and more versatile than nitroglycerin (NG) based products. These developments utilized various additives. These ingredients allowed various blends to be created with a wide array of physical properties and performance characteristics.
The new products gave the blaster the ability to custom mix products (See Figure 20.1) at the borehole and produce products with different properties and performance characteristics. Products with different velocities of detonation, density, and degree of water resistance then became possible. Bulk explosives changed the way explosives were delivered to the blast site. Ingredients could now be delivered directly to the blast site for mixing, custom blending and loading directly into boreholes. This reduced the manual handling of explosives.
This new wave in bulk explosive innovation caused a major change in the entire explosives industry. Bulk handling systems were required to transport and store the ingredients on the site. Over time it became economical to modify bulk truck systems and products to allow use of bulk explosives in smaller operations.
As explosive products were required to do more work, trucks offering more as a combination of component mixes became necessary to meet difficult blasting requirements. This generated a demand for new equipment to complement these new products and blasting technologies. Equipment operators needed the ability to mix and load custom formulated products with boreholes ranging from 75 millimeters to 500 millimeters (3 inches to 22 inches) in diameter or larger that meet demanding blasting requirements. Explosives and truck options must provide for borehole loading to match required product volumes, capabilities, and job complexities.
COMMON BULK TRUCK TYPES
The four common types of bulk trucks are (1) auger trucks, (2) pump trucks, and (3) multipurpose trucks (See figure 20.1). These are designed to deliver either pre-manufactured explosives or on-site manufactured explosive into the borehole. Within these types some are equipped to make ANFO or make blends.
AUGER TRUCKS
Auger trucks are used to mix and load ANFO and blends. Auger blends generally contain less than 50% emulsion. Auger loading trucks are available in several boom configurations, each having its own benefits for use. Auger trucks are available in any three basic auger discharge configurations (1) front over-cab discharge, (2) overhead rear discharge, or (3) side discharge. The most common of these boom configurations are discussed below.
Front Over-Cab Discharge
Front over-cab discharge auger, as the name suggests, has a discharge auger, which is over the cab of the truck. Cab-mounted controls permit the operator to position the truck, the boom, and load the product without leaving the cab. This combination saves time when positioning the truck and boom because of improved driver visibility and allows for one person operations. The boom discharges at a point above the height of the cabin through a flexible hose that can be moved from the boom end (See figure 20.2). This feature allows the truck to fill many boreholes without moving about on the pattern.
Overhead Rear Discharge
This style auger truck has a discharge located at the rear of the truck.
The boom discharges at a point about 2.4 meters to 3 meters (8 feet to 10 feet) above the ground through a flexible hose that can be moved (See figure 20.3). This feature allows the truck to fill many boreholes without moving about on the pattern. The discharge auger located at the rear of the unit causes operator visibility problems if the truck is fitted with in-cab controls.
Delivery rates of the overhead boom units typically range from 180 kilograms/minute to 680 kilograms/minute to (400 pounds/minute to 1,500 pounds/minute). Auger lengths vary from different truck or body manufacturers, however, lengths up to 6 meters (20 feet) are not uncommon.
Side Mount Discharge
Side boom units are equipped with augers or booms located on the driver's side of the truck. The auger swings about 180° off the driver's side (See figure 20.4). The boom discharges from a lower position to the ground than an overhead type and needs to be positioned directly over the borehole. These units are normally provided with in-cab controls to provide a one man loading operation. The higher delivery rate is a great advantage in maximizing borehole loading time, since the truck must be repositioned to load each borehole.
Delivery rates for side discharge units vary greatly depending on the sizing of the augers. These may range from 100 kilograms/minute up to 2,000 kilograms/minute (220 pounds/minute to 4,400 pounds/minute).
ANFO AUGER TRUCK
ANFO auger trucks (See figure 20.5) either load premixed ANFO into the borehole or they blend fuel oil with AN prill and then either auger or pneumatically load this mixture into the borehole. Beside the chassis and system controls, the fuel oil and auger systems are the critical components for this mixing systems.
BLEND AUGER TRUCK
By adding an emulsion or water gel tank and metering system to an ANFO auger truck, the truck becomes a blend truck (See figure 20.6), commonly referred to as a heavy ANFO truck. Blend auger trucks are similarly configured to ANFO auger trucks.
PUMP TRUCK
Pumping blasting agents has become very popular. Pump trucks (See figure 20.7) offer several advantages over using conventional packaged products. These include a reduction in finished product inventory and stocking requirements and an increase in cost savings. These trucks require high pressure with excellent vacuum characteristics to pass solids (prills, microballoons, etc.) without crushing them. Pump trucks are available in two styles, one that pumps a single product or another that blends emulsion and ANFO. When pump trucks are used for blending (See figure 20.7), the emulsion content is usually greater than 50% to provide a pumpable viscosity. These trucks contain an auger system to make the ANFO for blending.
Progressive cavity pumps are used almost exclusively to transfer the product because they meet the following requirements. The pumping system must be matched to the product viscosity, delivery rate, hose size, and distance the product is to be pumped. These requirements all relate to pump displacement, pump speed and pump pressure. Pumping usually requires pressures between 689 kilopascals and 1,380 kilopascals (100 pounds/square inch and 200 pounds/square inch). If this pressure cannot be attained or could damage the product a water or solution lubrication system may be required.
MULTIPURPOSE MIXING TRUCK
These trucks are offered to by various names by both the explosive supplier and the bulk truck manufacturer. These trucks are created by adding pumping capabilities to auger blend trucks. Multipurpose Mixing trucks (See figure 20.8) have a full range of product delivery capability. Because of their increased product delivery capability, they tend to be larger than standard auger or pump trucks and may have limited mobility for some applications. These styles of trucks generally have the highest quality controls due to the increase flexibility of the mixing or batching system.
TRUCK SELECTION CRITERIA
Bulk truck selection criteria are listed in table 20.1. All bulk loading units are selected for the product they deliver. After product selection is determined, bulk truck selection is based on the basic criteria in table and truck options discussed later in this chapter. Truck operating systems and safe operating procedures should always be considered first when selecting new bulk trucks or trucks to service an operation.
Bulk Truck Selection Criteria
Table 20.1 - Bulk truck selection criteria.
Borehole size and the pattern dictate the basic bulk truck body configuration, i.e., side boom or an overhead boom discharge may be required to load the boreholes efficiently. Specific types of trucks and blast sites may make these two criteria projects difficult.
Cargo carrying capacity is a very important consideration. It is directly dependent on the blast size, daily needs, and highway transportation limitations.
When using delivery rate as a selection criteria, a handy rule of thumb is to use one of the following two correlations between delivery rate and borehole diameter: (1) Auger delivery rates should be a maximum of 18 kilograms/minute or 2 kilograms/minute per millimeter of borehole diameter (100 pounds/minute to 150 pounds/minute) per inch of borehole diameter or (2) Pumping delivery rates should be a maximum .59 kilograms/minute to 1.34 kilograms/minute per millimeter of borehole diameter (50 pounds/minute to 75 pounds/minute) per inch of borehole diameter.
Transportation and storage of bulk blasting agent ingredients are not as many different ways. Since AN is the base ingredient in the above product types, economical sourcing of AN (prill) is essential as essential for optimal blasting economics. There are many AN plants in the United States and various other countries around the world. These plants vary widely in their production capabilities and capacities. Production capacities range from 50,000 tons/year to 565,000 tons/year. These plants are normally serviced by either railroads or roads that provide for fast, cost-effective distribution of these large AN production volumes to company locations and redistribution sites.
When AN prill is delivered, it is normally transferred into some form of on-site storage. This can be overhead storage bins, large bunker type storage, containers, bags, or directly into a delivery truck. Emulsion and water gels are manufactured in smaller satellite plants that are cost-effective to service regional areas. In the United States (as well as many other countries) bridge laws regulate the weights and payload of trucks traveling on roads.
BULK TRUCK SAFETY
Operating machinery presents inherent safety concerns and dangers. Bulk trucks are no exception. Bulk truck safety centers on personnel training and safety systems on bulk trucks. Table 20.2 describes the content of a recommended bulk truck safety-training program. The progressive cavity pump safety program addresses the safety issues peculiar to these pumps. This proposed program includes the content listed in table 20.2.
Recommended Bulk Truck Safety Training Topics
Table 20.2 - Recommended bulk truck safety training program topics.
A progressive cavity pump safety system is provided to quickly stop a progressive cavity pump and reduce the possibility of operator injury or other pumping hazards that may be created (e.g. a run-dry or deadhead condition is detected while pumping emulsion explosives). Progressive cavity pump safety systems must be part of the larger mechanical loading equipment safety program and be implemented as part of the overall explosive handling program. The training topics listed in the table 20.3 are recommended.
A Recommended Progressive Cavity Pump Safety Training Program
Table 20.3 – A recommended progressive cavity pump safety program.
These recommendations are made in consideration of the level of the hazard that may develop if either a run-dry or deadhead condition (can produce pressure maxima) which may promote overheating and transition to detonation is allowed to continue unchecked. Both of these conditions can produce dangerously high temperatures inside a progressive cavity pump, which may ultimately result in a catastrophic pump-hazard event.
GENERAL TRUCK OPTIONS
Blaster options to consider when selecting a specific truck include materials of construction, body capacity, body profile, chassis, general control systems, composition control, and accounting systems. All truck options and capabilities are summarized in table 20.4. An equipment capability analysis is further described in table 20.5.
Bulk Truck Capability Analysis
* Multiply by 3.28 for ft ** Multiply by 2.2 for lbs
Assumptions for bulk truck capability analysis:
Augered products:
- ANFO
- Blends <50% ANFO
Pumped products:
50% Emulsion or water gel
Chassis have a dry weight of 8.1 MT (18,000 lbs.)
All data in this table reflect standard type units sold in the United States with most frequently selected options.
Truck system options:
-
Control system
-
Weights & measures
-
DFO system
-
Emulsion/water gel tanks
-
Emulsion/water gel pump
-
Blend control system
-
Pumping system
-
Density control
-
Hose lubrication system
-
Hose reel system
-
Hammer mill
-
Additive feeder
-
Materials of construction
Product options: A. Ammonium nitrate B. ANFO C. High density ANFO (crushed AN prill or mini prills) D. Aluminum
E. Emulsion/water gel F. Density control G. Premixed pumpable wet hole products
Table 20.4 - Bulk truck capability analysis.
Bulk Truck Operational Equipment Analysis
Table 20.5 - Operational equipment analysis.
Materials Of Construction
Several metals are available for bulk trucks. Each has its own advantages and limitations. Many countries have codes or guidance notes, which indicate what type of material can be used when manufacturing a bulk truck.
Carbon steel has the lowest initial cost while offering good strength and ease of repair. This type of material is not allowed to be used for AN or emulsion bins in most countries.
Caution
In many countries, carbon steel is not allowed to be used for AN or emulsion bins.
Stainless steel is the ultimate material of construction. It has higher strength than carbon steel, is not affected by corrosive blasting agents and is easy to repair in the field. The surface of the material in direct contact with the flowing blasting agents becomes hardened producing a polished surface that enhances the flowability of the product. Stainless steel costs higher than carbon steel, however this material meets most of the requirements laid out by various code. The life expectancy of a body built of stainless steel is far longer than a body which would be manufactured out of carbon steel.
Because of its light weight, aluminum is a material used in the manufacture of bodies built to transport bulk blasting agents over the highway. Aluminum is also not affected by corrosive chemical materials. Aluminum has not been popular in off-road or pit-only applications as it does not respond well to high cyclic loading and it is also difficult to repair in the field. Aluminum is not as strong as steel. As a result, welded joints tend to crack more readily, requiring more frequent repair.
Capacity, Profile, and Chassis
Bodies are built in different length profiles. Typical units carry about 2.2 metric tons to 2.9 metric tons per meter of body length (about 0.75 ton (1 ton feet of body length). High profile units can carry about 2.7 metric tons to 3.7 metric tons per meter of body length (about 1 ton to 1.25 tons per foot of body length). If the units must be highway-driven in the United States, the Jovelin limits is influential because the unit must be long enough to distribute the load over the required distance to meet the Federal Bridge Laws. In addition, the center-of-gravity is lower for greater stability.
Examples of weight distribution by axle is illustrated in figures 20.9a and 20.9b.
Bulk truck and trailer capacity based on US Bridge Law maximum vehicle weight:
If the unit is to be used in an off-road application, a higher body profile may be desirable due to the higher load carrying capability. When selecting a body profile, the terrain of the blast site, the borehole pattern, and the availability of access roads must be considered.
Off-road chassis can be acquired with very high axle ratings allowing for maximum capacity. The chassis manufacturer's axle rating should not be exceeded.
Based on the U.S. Bridge Law, the preferred on-road model would have a low body profile, a front axle capacity of 9,070 kilograms (20,000 pounds) and a rear axle capacity of 15,420 kilograms (34,000 pounds). Additional pneumatic or air-ride axles may be added to increase the legal highway load carrying capability. Chassis are available with up to 38,555 kilograms (85,000 pounds) total rating in standard and can be custom built up to 56,700 kilograms (125,000 pounds) rating. Again, the chassis manufacturer's axle rating should not be exceeded. Please note that this only applies to the United States. Other countries have their own rules for on-road and off-road trucks and these need to be verified to ensure that the bulk truck meets all requirements before acquisition.
Caution
Countries other than the U.S. have their own rules for axle loadings and these rules should be reviewed before ordering a bulk truck.
The engine brake is also a desirable option to save brake wear and enhance safety. The overall net effective low gear ratio should be a minimum of 60:1 or higher. This low gear ratio allows easy movement of the unit between bore holes with a minimum drive line damage and clutch wear. Diesel engines are the only engines allowed in most countries.
The requirement to open and close tank valves and vents and blow out hoses requires an air compressor with a minimum output of 450 liters/minute (16 cubic feet/minute).
General Control Systems
Control systems on a bulk truck range from finder-mounted manual control systems for product run and boom movement functions to in-cab-closed loop control systems. Trucks can also be provided with both outside and in-cab controls or remotes. The current range offered from various manufacturers throughout the world is endless and meets many different needs.
A cab-mounted control system allows operation of the unit to be controlled from the cab. The cab control feature is also desirable in adverse weather conditions. This system also allows utilization of a set of manual controls on the fender or in a bucket system in case there is some form of failure of the electric or air portion of the control circuit. After optional controls may be added to the in-cab systems. These include a predetermined counter to stop augers automatically after loading a preset amount of product in a borehole. The more advanced bulk trucks now have computers onboard.
These programmable controllers allow the operator to input a formula, quantity, and rate of delivery. Then the unit loads the hole with no other operator involvement. This system can also be programmed to indicate if the product is not within an acceptable specification range. The programmable controller gives the blaster an endless selection of formulas, rates, and information storage, download and hard copy printout capability. The computer control systems can allow for data transfer through a cell phone modem, satellite phone or radio. This feature allows the loading instructions and the quantity loaded to be transferred to the mine office or other desired location.
Composition Control and Accounting System
There are two reliable methods of monitoring the quantity and composition of products mixed or blended on bulk trucks. The first relies on counting the number of revolutions (the AN prill auger system turns and the number of revolutions the emulsion or water gel pump turns in the same period of time or at the same borehole. When the quantity (kilograms, pounds) of AN prill per-auger revolution and the quantity (kilograms, pounds) of emulsion-per-pump revolution have been measured in advance, the total of each per hole, and therefore the ratio, can be calculated. This is a cost-effective method of monitoring product delivery rate and ratio.
A set of battery-powered or mechanical totalizers can also monitor AN prill, emulsion or water gel delivered. This package is inexpensive and when used over a measured period of time provides the same information as tachometers, and can also be used as a backup system for the entire job or period total. There are also time-based systems utilizing clocks. This system allows the operator to run devices at a fixed speed over a given time to generate an amount of product delivered. Popularity of this system has faded due to new electronic options available. The accuracy of calculations of this technology relies upon flow meters installed in the liquid product stream. The output from these meters is read by the computers control system and the product streams are adjusted to a set point producing the desired formula.
The second system employs an on-board weighing system. This measures total product weight in the body and, as product is delivered, can accurately fill each hole with a measured amount of product. This system is available to weigh the complete body or can be mounted to weigh the emulsion tank separate from the ANFO body. These scales can also be equipped with an in-cab printer for hard copy records. An on-board weighing system, however, is expensive and requires more maintenance than the other simpler system.
Fuel Oil System
Fuel is added to ammonium nitrate prill to produce ANFO. A fuel system allows the mixing to take place at the borehole as the product is loaded. It consists of a fuel tank of suitable size (6% of the ammonium nitrate by weight + 20% reserve), a FO pump, a flow meter totalizer, and injection nozzles for dispensing the FO into the AN prill. The pump must be tuned to the metering auger. The pump may be chain driven or mechanically coupled to the bottom auger or driven more precisely by a hydraulic control system.
Auger System
AN prill and ANFO can be measured while being loaded with an auger (See figure 20.10). An auger is a helicoidial device of a fixed pitch (distance between flights) and fixed diameter. As the auger turns it generates a fixed displacement volume of material being conveyed. By counting the number of times the auger turns and relating this to product density the mass of the product being delivered can be calculated. Notice the pitch angle toward the discharge end of the auger changes to speed the flow of product from the auger and maintain the flow of product.
Pneumatic Loading System
A pneumatic loading ANFO system is sometimes referred to as a blower system. This system uses large volumes of air to force the ANFO mixture along a loading hose. An auger drops the mixture into an air lock, which in turn drops the product into the air flow. This type of discharge system is generally used when a small amount of product is loaded into a large number of boreholes.
Blend Control System
The use of multiple product streams leads to the requirements for more complete control systems. There are many different types of control systems used in the industry today. These controls vary greatly among users, manufacturers, and countries. Following are descriptions of three types of blend control systems: (1) ratio control, (2) speed control, and (3) closed loop system.
Ratio Control System
The first system is a ratio control concept. In this system each product stream is set in ratio to another product stream or the finished product, for instance, FO 6% of AN prill and emulsion 30% of total of products. The total product delivery rate is then adjusted by truck engine speed. For example, the following engine speeds may have the indicated delivery rates: (1) engine speed of 1,000 revolutions/minute (rpm), might have a delivery of 45 kilograms/minute (1,000 pounds/minute) or (2) engine speed of 1,500 rpm might have a delivery rate 680 kilograms/minute (1,500 pounds/minute). This system is by far the oldest of the modern control systems and accuracy relies on correct engine speed and operator input.
Throughout the delivery range, the product streams stay in ratio to each other without additional adjustment. The primary benefit of this system allows the augers to maintain a constant speed percentage of fill to ensure proper mixing. It also keeps auger clogging to a minimum.
This system allows the shot designer to select the ratios of product to be delivered and the operator to vary the loading rate to match the borehole loading conditions. This system may be set with two or three preset ratios depending on the product to be delivered.
Speed Control System
The second system utilizes an independent device to control the speed of each function (i.e., FO, aluminum, AN prill, emulsion, bottom auger, vertical auger, or top augers). When this system is utilized the rates of ingredient streams, percentages of auger fill, and total product delivery rate are interdependent. If any of these items change, a review of the change must be evaluated and changes to the other items must be made to keep the system in balance and yield the desired results. This system is very precise and can be calibrated accurately allowing for an excellent degree of control, but is also the most complex to operate and cumbersome if products and rates must be changed often. These systems most often require a piston type hydraulic pump, which is very efficient.
Both control systems have advantages and disadvantages that must be considered for any particular application.
Closed Loop System
The third system is by far the most advanced and is called closed loop control. The basis of this system is a programmable logic controller (PLC) or personal computer (PC). In this system, each device is controlled separately and has its own hydraulic flow control. The hydraulically driven devices, through a sensor system, feed their speeds into the controller that, in turn, sends a signal back to the hydraulic system allowing it to make necessary changes to the speed of the driven component. This system may also monitor the actual product stream and send a signal to the controller to adjust the hydraulic flow rates to the device driving the pumps, augers or mixing devices. This sampling and speed adjustment takes place several times per second.
The main advantage of this system is that it allows the operator to produce almost any product regardless of the number of ingredients, and allows the machine to monitor itself to yield optimum quality control.
The controller can also drive a printer to provide a hard copy of daily activity. This system may also interface with a laptop, printers, telephone modem or radio for borehole loading information and the same devices can also be used to do data acquisition after the boreholes are loaded. The major disadvantage of this system is the initial expense and difficulty in troubleshooting.
Flow Measurement System
Product and material density must be measured on a regular basis to ensure that flow meter calibration factors remain valid. Pumps and augers produce a volume of product every revolution. Density has no effect on the volume displaced, but effects the weight of the volume.
The data from flow measurement devices is used to set the "calibration" of the auger and pump. The ratio of the speeds and displacements of the rotary devices yields a percentage of each ingredient in the finished product, allowing the operator to produce the required mixture. Operators may contact the bulk truck or explosives supplier for full instructions on how to perform this task on the specific piece of equipment using actual products to be loaded.
Optional Systems
The hammer mill and additive feeder are used to modify the bulk product ingredients to give the final product additional physical properties and performance characteristics.
Hammer Mills
A hammer mill is a rotary crushing device utilized to crush AN prills to increase their bulk density (See figure 20.11). These units are used to make specialized and blended ANFO, emulsion and water gels.
Additive Feeders
Additive feeders (See figure 20.12) are used to add small amounts of solid materials into the AN prill stream to enhance energy or alter density. The most commonly used additive is aluminum.
Blend and Pump Truck Systems
These trucks pump a pre-manufactured product which can be straight or blended emulsion. These trucks have an ability to blend emulsions. Trucks commonly consist of a single tank for the storage of the emulsion/water product, pump hose reel, water metering and additive systems.
Products may be premixed and then loaded into a pump truck whose only function is to pump this product into a borehole.
A second system utilizes a bin's body that is usually blend and mix multiple product streams together, discharge them into a hopper mounted above or in close proximity to the pump, then pump the product down the borehole.
These units are easy to operate and give the maximum flexibility in custom borehole loading because only a small quantity is being mixed continuously at any time allowing formula changes to be made as required.
Emulsion and water gels can be measured while being loaded with a fixed displacement pump. The pump is normally a progressive cavity or lobe type device. As the pump turns it generates a fixed displacement volume of material being conveyed. By counting the number of times the pump and relating this to product density the mass of the product being delivered can be calculated.
Emulsion Or Water Gel Tanks
Tanks are offered in a variety of sizes and configurations for on and off-road use. It is important that the sump area be so small as possible to reduce the chance of product build up as a tank level. Insulation and heating coils may be added depending on the climate and requirements of the products handled. A top loading hatch cover flat is easy to operate is a very desirable feature. Valving of the tank must be of suitable size in diameter to enhance product flow and reduce pump suction requirement. Tanks must be built to meet requirements of the application. The United States Department of Transportation and many other countries have laws and regulations that dictate how these tanks must be built and tested.
Emulsion Or Water Gel Pumps
When emulsion or water gel is added to ANFO to make a blend it is transferred from its tank into the delivery auger for mixing. Typically, emulsion or water gel is pumped with either a gear/lobe or progressive cavity type pump. The addition of pumps for blends requires the addition of safety devices.
Gear/Lobe Pumps
These units are equipped with two rubber coated gears (See figure 20.13), one driven by a hydraulic motor and the other gear driven by the first gear. Gear pumps are inexpensive and provide a good form of metering for manufacturing blends of emulsion/water gel and ANFO. They are designed to produce about 689 kilopascals (100 pounds/square inch) of product pressure, which is sufficient to inject most products into the mixing chamber. The primary advantages to these pumps are low cost, light weight, and small physical size.
Caution
Gear/lobe pumps are unsuitable when water gel contains AN prill as the prill causes high wear on the gear components.
Caution
Gear pumps are unsuitable when water gel emulsion contains AN prill as the prill causes high wear on the gear components.
Progressive Cavity Pumps
These units incorporate a corkscrew type rotor that turns inside of a rubber stator to produce a moving cavity (See figure 20.14). This design is more expensive but yields excellent metering capability. A progressive cavity pump will produce about one full atmosphere of vacuum. Depending on the length of the rotor and stator, these units can produce up to 2,070 kilopascals (300 pounds/square inch) of product pressure. The primary advantages of these pumps are excellent suction characteristics, good metering and high-pressure capability.
Due to the potential problems of material damage or other pumping hazards, consult the explosives supplier for the recommended pump that provides protection against overpressure and prevents loss of product flow. Regular, scheduled maintenance is also important to assure safe operation of progressive cavity pumps.
In a further effort to assure safety and minimize liability, the bulk truck suppliers have developed universal pump safety systems. These safety systems have been developed in an effort to address the identified hazards and to meet the standards imposed by the explosives suppliers including best practices required in the countries where the equipment was to be used. Each pump manufacturer uses their own technology to address and protect against common operating requirements. The requirements should protect against the factors in table 20.6.
Pump Requirements For Pump Hazard Protection
Table 20.6 – Pump requirements for pump hazard protection.
Hose Reel System
Hose reels (See figure 20.15) are generally required on a bulk truck which pumps product along a loading hose and into a borehole. There are many different hose reel designs available. The design depends on the borehole diameter, borehole depth, and the specific requirements of the user.
Hose reels can be mounted at the rear of the cabin or the rear of the body. A typical hose reel utilizes a boom that extends about 0.9 meters to 1.8 meters (3 feet to 6 feet) off the cab, or rear of the unit. These heavy duty units operate at 0.75 millimeters (3 inch) inside and a .56 millimeters (2 inch) discharge. Also available is a hose reel design with the same basic specification except the boom extends up to 3 meters (10 feet) from the center line of the truck. This hose reel boom swings a full 180° above the rear of the truck allowing the operator to load several boreholes without moving the truck.
A depth gauge may be built into these hose reels allowing the operator to use the hose to measure the borehole depth, offering good feedback as to the location of the hose and relative to the product as the borehole during the loading process.
Density Control System
Density control is a way to increase the sensitivity of the product by adding a gassing agent, microballoons, or other lightweight substance to the product.
Gassing agents have been used successfully, requiring one or two additional liquid streams to be metered and injected into the primary product stream. These agents mix together and produce evenly distributed small gas bubbles reducing the product density.
Solids, such as microballoons, can be added in the product are loaded. This practice is used on a limited basis due to the high cost of the materials.
Hose Lubrication System
This system has become extremely popular to reduce pumping pressures. The system utilizes a ring after the product pump with a small annular space to inject a solution into the hose as a film between the hose and the product being pumped. The solution forms a barrier marshaled as velocity to the product being pumped, producing an easily sheared film allowing the product to slide down the water-lined hose. Lubrication can reduce product pumping pressure by as much as 80%. The solution required is about 1% to 3% of the weight of the product being pumped. Although water is the most commonly used lubricant, other fluids can be added to reduce the pumping pressure even more, but compatibility must be checked with the explosives supplier prior to using any additives.
Gassing System
The gassing system (includes a tank(s) suitable for the agent(s) to be used, a metering pump, a control system, a flow meter and a mixer of suitable design to assure the agents are dispersed evenly through the product. This system may use one agent or two agents depending on the technology of the explosives supplier.
REFERENCES
International Society of Explosives Engineers. 1998. ISEE Blasters' Handbook™, 17th Edition, Cleveland, OH.