Chapter 22: Mini-Bulk Pumping Systems
There are many different types of mini-bulk loading systems. Commonly these systems are not an integral part of the prime carrier (chassis) or have capacities of more than 2 tons. Larger capacity systems that are attached to the prime carrier are considered standard bulk trucks. These mini-bulk systems are very portable (See figure 22.1) and fill a need in the industry for cost effective loading in small diameter, small volume applications. Most of these systems also provide a means of remote control allowing the blaster to control the loading process from the borehole.
CAPABILITIES
In construction applications where it is common to need small quantities of explosives, the use of some of the mini-bulk equipment has allowed bulk to be used without the costs associated with a large bulk truck that would be under utilized. These construction applications may also have problems getting large equipment to the actual pattern. In those situations it is not uncommon to either carry the packaged materials to the pattern manually or have those materials brought up with a loader. It can be much easier to have the construction equipment either pull or carry the mini-bulk equipment to the pattern. In underground and shaft loading applications, where there is limited access to the working face, many of these mini-bulk systems are ideal.
The advantages of loading bulk explosives as compared to packaged explosive products are well documented. Savings in labor costs associated with handling packaged materials, the reduced labor needed to load a blast and the ability to completely load a borehole, thereby fully utilizing that borehole's potential, is understood. With these advantages and the improvements in bulk loading technology that have occurred, the utilization of bulk loading has moved into smaller volume applications. Additionally, with the current emphasis on being green, the elimination of the initial packaging and the disposal of the used packages is an advantage.
However, there are some aspects of loading in these smaller applications that need to be understood. With the growing emphasis on accurate records, it should be noted that obtaining very accurate usage weights might require taking additional scale weights, which were not needed when using packaged products. In some cases, one of the major advantages of loading bulk explosives – better coupling and higher loading density leading to fewer holes – can be a disadvantage when the pounds per delay and the associated impacts (air overpressure and vibration) are of primary importance. Additionally, many bulk explosives, in particular water based emulsions, slurries, and suspensions have a larger critical diameter than can easily be accommodated in some small boreholes.
Given these advantages and disadvantages, bulk loading has proven to be useful in many blasting applications including construction, shaft sinking, underground, and underwater loading from drill barges. While some of these applications are not new, for instance loading bulk ANFO and emulsion underground has been used for decades, the wider acceptance in other applications is growing.
Selection of a mini-bulk loading system begins with identifying the explosive product performance characteristics required for the job, and shot requirements and operating space available. Selection criteria are summarized in table 22.1.
Mini-Bulk Loading System Selection Criteria
Table 22.1 – Mini-bulk loading system selection criteria.
PRODUCT PERFORMANCE CHARACTERISTICS
Begin the mini-bulk system selection process by identifying the explosive product performance characteristics required by the job. Are the boreholes wet or dry? If the boreholes are dry, pneumatically loaded ANFO can be used. If the boreholes are wet, then a water resistant product such as an emulsion, suspension or gel is the choice. Next consult with the bulk explosive manufacturer to ensure the critical diameter of the product used in the mini-bulk system is smaller than the expected borehole diameter. Additionally, pre-compression resistance is a common requirement in the applications where mini-bulk systems are most useful. For instance, tight patterns and wet rock produce ideal conditions for dead pressing.
LENGTH AND DIAMETER OF HOSE
Once a product is identified, the loading application needs to be considered in determining what mini-bulk system should be used. As most of these products will be loaded using a hose, consideration must be given to the length of loading hose needed and its diameter. In most mini-bulk applications, it is common for the loading hose to be handled manually, so its weight is a consideration. Common loading hose diameters are 19 millimeters (¾ inch) to 1½ inches, with the weight per foot of the 31.8 millimeter (1¼ inches) loading hose being almost three times as much as the 19 millimeter (¾ inch) loading hose. The delivery pressure also impacts the delivery rate and length of loading hose. In mini-bulk systems that do not utilize a water lubrication system to reduce pumping pressures, the maximum length of the loading hose is directly related to the hose diameter and loading pressures. The trade-off is that the larger the diameter of the loading hose, the heavier it is, but the longer it can be. The length of loading hose that can be effectively used without a water lubrication system is between 15.2 meters to 30.5 meters (50 feet to 100 feet) depending on the hose diameter, pressure and the rheology of the bulk product used. The delivery pressure also impacts the delivery rate and length of loading hose. The use of a water lubrication system allows loading hose lengths of more than 45.7 meters (150 feet), while maintaining acceptable loading pressures and rates. However, water lubrication adds a level of complexity to the system that is not needed in many applications.
CHASSIS TYPE
Additional equipment considerations include: the possible need for skid mounting if the system will be pulled around a pattern, adequate structural integrity required to be lowered into a shaft and regulatory requirements if the system will transported on public roads. This type of delivery system, illustrated in figure 22.2, typically has a capacity up to 2,000 kilograms (nearly 2 1/4 tons) and utilizes 60 meters (200 feet) of 25 millimeter (1 inch) diameter hose with a pumping rate of about 70 kilograms (150 pounds) per minute (See figure 22.2).
HOLDING TANK CAPACITY
The capacity of the mini-bulk system is a consideration. Mini-bulk systems can have a capacity of less than 225 kilograms (500 pounds) to as much as 1,841 kilograms (4,000 pounds). Larger capacity means a physically larger system that is more difficult to move. The size and lifting capacity of the equipment used to lift or move the system is also a factor in determining the capacity. The primary consideration is the expected volume demand – either per round or shot on a daily basis. The capacity should always be larger than the expected loading requirements for any single shot or round. Leaving the pattern to reload is inefficient.
Many of the storage containers are considered intermediate bulk containers (IBCs) and can be tested to a published standard. In some cases the storage is non-specification, which is not built to an established specification. When the system is transported on public highways there may be additional requirements. In all cases, it is critical to ensure compliance with all regulations regarding storage, handling, and transportation of the explosive materials.
POWER SOURCE
The next equipment selection consideration is the source of power for the mini-bulk system. Most mini-bulk systems are either pneumatically or hydraulically powered. The advantage of the pneumatically powered systems is that most operations (underground, shaft or construction) have a ready source of air. Most of these systems operate within the typical pressures and flows that are common in these applications. These systems are typically less sophisticated, but easier to operate. Hydraulically powered units can be more complex, often utilizing a water lubrication system, but are required to have a source of hydraulic power attached to the system. Electrical power may be needed for some systems. These electrical demands are usually low and can be obtained using a battery or small generators that can be powered either pneumatically or hydraulically.
PRODUCT DELIVERY METHOD
The method of product delivery is also an important consideration. Products can be pumped using several types of pumps, blown as in the case of pneumatically loaded ANFO, or the product can be moved through the loading hose using a the pressure from a pressurized storage container. Each type of pump has advantages, disadvantages and different safety requirements. Whenever pumping or moving explosive materials, full compliance with the loading recommendations and safety systems designed by the explosive and mini-bulk system manufacturer must be maintained.
Progressive Cavity Pumps
These pumps require a motor to turn the pump. This motor can be either pneumatically, or more commonly, hydraulically powered. Progressive cavity (PC) pumps can be high volume and high-pressure pumps. It is common to use water lubrication with these pumps. PC pumps require a pump safety system as recommended by the explosive and equipment supplier. There will be some electrical requirements to operate the pump safety system. PC pumps are excellent metering pumps and can give very accurate poundage readings if calibration is maintained.
Piston Pumps
These pumps require a motor to run the pump. This motor can be either pneumatically or more commonly hydraulically powered. Piston pumps can be high volume and high-pressure pumps. Piston pumps require a pump safety system as recommended by the explosive and equipment supplier. There will be some electrical requirements to operate the pump safety system. Piston pumps can be excellent metering pumps and can give very accurate poundage readings if calibration is maintained.
Air Diaphragm Pumps
These pumps typically only require an adequate air supply to operate properly. Air diaphragm pumps can be high volume and high-pressure pumps, although these pumps may not generate as high a pumping pressure as PC or piston pumps. Air diaphragm pumps do not require a pump safety system as long as the air used to power the pump is properly regulated. As the pounds per cycle can vary depending on discharge pressure, air diaphragm pumps are not as good as PC or piston pumps for accurately determining loading poundage. Mini-bulk systems with these pumps are typically simpler to operate than systems using PC or piston pumps.
Pressure Delivery Systems
Pressure delivery systems require only an adequate air supply. Unless an additional air compressor is used, these delivery systems are pressure limited to the air pressure available at the mine or job site (typically 725 pounds/square inch (862 kilopascals)). It is not common to use water lubrication with these pumps. Pressurized delivery systems are the least accurate for determining loading poundage. Pressure delivery mini-bulk systems like that shown in figure 22.3 are typically very simple to operate.
There are many different features on mini-bulk loading systems that provide a wide range of flexibility in loading. With these mini-bulk systems, small-diameter and small volume users have a tool that can help to make them more effective. The use of mini-bulk systems is growing as different applications are identified. While packaged products will always have a place, these systems are making that space smaller each year.