9638G

PUMP SAFETY TESTS REGARDING EMULSION EXPLOSIVES

Hans PerlidNItro Nobel AB / Dyno Explosives Group

Gyttorp, Nora, Sweden

ABSTRACT

In the handling of emulsion explosives pumping is a key operation. A number of serious accidents has shown that pumping can be a risky operation and should be carefully considered and investigated. This is the background behind a series of pump tests carried out by NITRO NOBEL.

This paper refers to pump safety tests with an eccentric screw pump (progressive cavity) and emulsion explosives. A Selection of emulsions unsensitised as well as sensitised were tested. The tests were performed in a circulation system against dead head and as dry pumping.

Temperature, pressure, and speed sensors delivered signals to a data scanner and the datas were continuously monitored on a PC. (Fig. 1) The stress on the different emulsion products was relatively high during the tests. The pumping continued for 30-50 minutes, at pumping pressures up to 27 bar and temperatures above 150 °C. All tests were performed at a pump speed of 200 rpm which is the highest recommended speed (by FEEM*) for these type of pumps when pumping emulsion explosives. *FEEM = The Federation of European Explosives Manufacturers.

16 pump tests were carried out with 6 different emulsion products and powerful reactions were received in 4 tests.

When dry pumping a mix of 20% ANFO and 80% bulk emulsion matrix a quick and powerful temperature rise (800 °C) started after 30 min. in the pump housing. All rubber parts and the emulsion mix in the pump housing were destroyed. (Fig. 3)

The second dry pumping test with microsphere sensitised product of the 20/80% mix as above gave a very powerful increase of temperature (1000 °C) after 42 min. All rubber parts and the emulsion product in the pump housing as well as the stator burned out. (Fig. 5)

By dry pumping cap sensitive emulsion containing wax, an explosion occurred after 35 minutes in the outlet pipe. The reaction started in the pump stator, accelerated and finally exploded in the cut-off valve about 700 mm from the pump outlet. (Fig. 6,7) The cut-off valve was open during the dry pumping test. The pump was slightly damaged and the piping behind the valve was found 10 meters from the pump.

Copyright © 2000 International Society of Explosives Engineers1996G - PUMP SAFETY TESTS REGARDING EMULSION EXPLOSIVES - P 101 1 of 12

The test was repeated and an explosion occurred after about 35 minutes of dry pumping. This explosion was more powerful and destroyed the piping completely. The detonation splitted the pump stator but stopped in the middle of the stator. The reaction probably again started in the pump stator, accelerated and then detonated somewhere in the pipe system. (Fig. 8,9)

PUMP TEST EQUIPMENT

The tests were performed in one of Nitro Nobel's test tunnels and were remotely controlled from a room outside the tunnel.

The tested pump was a two stage eccentric screw pump (progressive cavity) with a solid, undersized (60 °C) and hard chromium plated rotor having a diameter of 30 mm.

The stator was standard with nitril rubber, the joints withpin-type sealed couplings and the seal of mechanical type. The drive unit was electrical with a belt variator. The piping was stainless steel 40 mm x 2,6 mm and the shut off valve a stainless steel ball valve 1 1/2". The datas were sampled by a 8 channel data scanner with 10 readings per second. Silicon insulated and compensated thermocouples cable type K were used for the temperatures and thin film sensors for the pressure.

PUMP EQUIPMENT SET UP

The eccentric screw (progressive cavity) pump was connected to a stainless steel circuit from the outlet and to the top of a vessel. See Pump test set-up, Fig. 1.The vessel had a volume of 30 litres and was mounted on the top of the pump inlet. The total length of the piping including the shut off valve was about 2 meter. The shut off valve was located 700 mm from the pump outlet.

Two temperature sensors were mounted at the pump stator, one 30 mm from the beginning- (T1) and the second (T2) 30 mm from the end of the stator. Holes for the sensors were drilled in the stator down to 2 mm from the inside. One temperature sensor (T4) was mounted inside the pump housing. The fourth (T3) was mounted at the bottom of the vessel. The fourth temperature sensor (T3) was in the second test series (double tests) mounted in the piping about 200 mm from the outlet of the pump.

One of the pressure sensors was mounted in connection with the pump housing (P1) and the other (P2) about 100 mm from the outlet of the pump.

PUMPING PROCEDURE

Pumping against dead head: The vessel was filled with approximately 15 kg of the tested product. The pump was started and the product was circulating until the whole


pipe system was completely filled with product. The pump was shut down and the shut off valve closed. The data system was loaded and the pump was remotely started.

Dry pumping: The vessel was filled with approximately 15 kg of the tested product. The pump was started and the product was circulating until the pipe system was completely filled with product. Then the pump system was emptied by pumping and when empty, the pump was shut down. The data system was loaded and the pump was remotely started again but this time with the shut off valve open. The product remaining in the system was located in the pump housing, very little in the stator and a considerable amount in the piping.

REFERENCE TEST WITH WATER

The reference test with water was done to investigate the influence of the friction between the stator and the rotor.

Against dead head: The test continued for 30 minutes and the increase of temperature in the stator was 10 - 15 °C. Much water is recirculating in the stator because of the back pressure and the poor lubrication between stator and rotor when pumping water. Accordingly the water acts as a cooling medium during the test. The pump pressure started at about 10 bar and ended at 14 bar. The pressure increase was caused by the temperature increase. The rotors in all tests were undersized (60 °C) and the pump was designed for 12 bar when pumping water.

Dry pumping: The dry pumping with water was severe and already after 6 -7 minutes smoke came out from the pipe. The pumping continued for 21 min and the increase of temperature was more than 100 °C in the end of the stator. (Fig. 2) The stator was completely burned out after the dry pumping.

BULK EMULSION MATRIX

The pH of the matrix was decreased to cover even matrix for chemical gassed bulk emulsion. This emulsion was a single salt bulk emulsion matrix with a water content of about 15 %.

Against dead head: The pumping time was 30 minutes and the temperature rise in the stator was about 80 °C. The temperature of the emulsion was 60 °C when the test started. The pump pressure oscillated between 15 and 25 bar. The stator was intact after the test.

Dry pumping: The dry pumping of the same bulk emulsion matrix continued for 35 min and the temperature rise in the beginning of the stator was about 90 °C. The pump stator was intact also after this test. The lubrication effect is very good for this product.


MIXED BULK EMULSION MATRIX

The tested bulk emulsion matrix was made from a two salt oxidizer with low pH (the same as for chemical gassing). The matrix contained 80 % emulsion and 20 % ANFO.

Against dead head: A temperature increase was noticed at T4 in the pump housing after 15 minutes, but nothing more happened during the 37 minutes of dead head pumping.

Dry pumping: The dry pumping of the mixed bulk emulsion matrix (Fig. 3) was shut down after 27 minutes because of high temperature at T4 ( 200 °C ). After shut down the increase of temperature continued and rose to more than 800 °C. Finally the pump cooled down without any more reaction. The pump was inspected and all rubber parts and the bulk emulsion had burned out.

The pump test with Emulan 8000G matrix was repeated because of the burn out in previous test 4. None of the dead head or dry pumping tests did show a similar reaction this time.

MATRIX FOR CAP SENSITIVE EMULSION

This matrix was a typical emulsion matrix for cap sensitive emulsion explosive including wax and aluminium and with a water content of about 10 %.

Dry pumping: The temperature increase of T2 was 60 C after 35 minutes of dry pumping.

Against dead head: The dead head pumping was very difficult with this product because of high solidifying point. The dead head pumping tends to be dry pumping after a short time. Steam- or hot water tracing at the pump is necessary for this product and that was not possible to arrange.

BULK EMULSION EXPLOSIVE

This test was with a single salt (AN) bulk emulsion sensitised with glass microspheres. The water content was about 15 % and the hot density for the tested product was 1,14 g / cc.

Against dead head: The temperature in the pump housing increased from 45 C to 135 C in 35 minutes. The pumping pressure pulsated between 15 and 23 bar. (Fig. 4)

Dry pumping: The dry pumping of this explosive product did not show any reaction


and the stator was intact after the test. The lubrication effect is good for an oil based bulk emulsion. The pump test of the bulk emulsion matrix ( No. 2 ) did show the same lubrication effect.

MIXED BULK EMULSION EXPLOSIVE

The mixed bulk emulsion explosive was a mixture of 75 % microspheres sensitised all AN- emulsion with a hot density of 1,14 g/cc. mixed with 25 % ANFO. The hot density for the mix was 1,23 g/cc.

Against dead head: T4 increased from 60 to about 135 °C after 23 minutes. The pumping continued for 13 minutes without severe effects. The pumping pressure fluctuated between 14 and 22 bar. Dry pumping: The dry pumping passed without much reaction.

This product is very common and widely used and therefore it was decided to repeat the test. The dead head pumping resulted in a temperature increase after 25 minutes. Ten minutes of further dead head pumping passed without reaction.

The dry pumping was more dramatic: The pump burned out after 40 minutes. Of course this type of dry pumping is an abnormal handling of the pump and a burn could have started in the rubber parts of the pump without reaction in the emulsion product. (Fig. 5)

CAP SENSITIVE EMULSION EXPLOSIVE

The cap sensitive emulsion explosive contained wax, 5 % of aluminium and was sensitised with microspheres to a hot density of 1,13 g / cc.

Dry pumping: The dry pumping was the only test done because of the solidification problems for this kind of product. In the beginning of this test the highest temperature was measured at T2. The temperature at T2 increased from 40 °C - 135 C in 34 minutes.

Suddenly after nearly 35 minutes of dry pumping an explosion occurred in the equipment. (Fig. 6,7) The communication with the pump was still OK, and the pump continued to run at 200 rpm, so the explosion was figured to be limited. The inspection afterwards showed that an explosion probably occurred in or exactly after the shut off valve. The pump was slightly damaged. One of the pump stands was broken and the bolts to the rotor couplings were bent. The piping after the valve vas found about 10 meter away from the pump. The reaction probably started in the pump, accelerated and finally went to a small explosion. The amount of exploding product was calculated to about 20 grams.

A new test with identical cap sensitive explosive was carried out with the following


results: Dry pumping: Again an explosion occurred after about 35 minutes of dry pumping. This explosion was much more powerful and destroyed the piping completely. The pump was badly damaged and the detonation splitted the pump stator. The detonation stopped in the middle of the stator and the emulsion product in the pump housing did not detonate.

As before, the reaction probably started in the pump stator, accelerated and detonated somewhere in the pipe system. The pipe system was completely destroyed and the thickness of the pipe parts was only a few tenths of a millimetre. The original pipe thickness was two mm. The reaction started after 34,5 minutes and the temperature at T3 increased to 300 °C in about 12 seconds. Then it cooled down to 200 °C and again very rapidly increased to more than 500 °C. Again it cooled down and suddenly after 35 minutes and 40 seconds it exploded. (Fig. 8,9)

The reason for the strange temperature fluctuation was probably that hot particles came in contact with the temperature sensor for short moments. T3 was in this second test mounted in direct contact with the tested product, in the outlet pipe about 250 mm from the pump outlet.

CONCLUSION

These pump tests show that it is quite possible to create a detonation by wrong pump handling while pumping cap sensitive emulsion. A temperature rise of ca. 800 °C was measured when pumping a bulk emulsion matrix containing 80% ANFO. This reaction did not result in a detonation. The most serious reactions occurred when dry pumping. However, dead head pumping can also cause serious reactions. As shown in the enclosed list regarding accidents with waterbased explosives, pumping is often involved.

Recommendations:

BE CAREFUL IN YOUR SELECTION OF PUMP TYPE AND MANUFACTURER. MAKE WRITTEN RULES AND TRAIN/EDUCATE YOUR PERSONNEL.

AVOID OVERSIZING THE DRIVE UNIT AND LIMIT THE TIP SPEED OR RPM.

REDUCE/ LIMIT YOUR PUMPING PRESSURE.NEVER RUN THE PUMP AGAINST A DEAD HEAD.ENSURE THAT MATERIAL FLOWS THROUGH YOUR PUMP.

RUN REGULAR SERVICE INTERVALS WITH AUTHORISED PERSONNEL USING ORIGINAL SPARE PARTS


ACCIDENTS WITH WATERBASED EXPLOSIVESIn operations related to manufacture and burning.

1966 USA Premix 2 killed1966 USA Slurry, pump1973 Norway Premix 5 killed1974 USA MMAN, transport 2 killed1975 Canada Powermex, cartridging 8 killed1976 USA MMAN, pumping1976 Sweden Slurry, burning1977 Japan Slurry, burning1981 Switzerland MMAN1984 France Slurry, fire1987 South Africa Tovex, manuf. 5 killed1988 Sweden Emulsion, burning1988 Canada Emulsion, pumping 4 killed1989 France MMAN- slurry, mixing1990 Canada Emulsion, pumping1990 South Africa Emulsion, pumping1990 Russia Emulsion 16 killed1990 South Africa Emulsion, pumping1991 China Emulsion, pumping 7 killed1993 South Africa Emulsion, burning1994 Papua New Guinea Emulsion, pumping 11 killed1995 Sweden Emulsion, burning

References:

1. Rock Blasting and Explosives Engineering. Per-Anders Persson, Roger Holmberg and Jaimin Lee2. Safex reports.


Figure 1 The temperature sensors T1, T2 and T4 are in the same position for all tests. T3 is located in the bottom of the Emulsion vessel in the first series of tests. The second series is the double tests of Mixed Bulk Emulsion Matrix, Mixed Bulk Emulsion Explosive and Cap Sensitive Explosive.

This water test show that this pump type create high temperatures caused by the friction.


The pump was shut down after 27 minutes, but the temperature continued to increase.

This chart show that a 2-stage PC pump is capable to a high pressure when pumping emulsion.


T3, in the outlet pipe of the pump showed a very high temperature rise after 42 minutes of dry pumping. The rubber parts in the pump were burned out.


This chart show the time for the explosion in the first of the tests withcap sensitive emulsion explosive. The explosion happened after 34 minutes and 48,8 seconds of dry pumping.

The explosion/detonation in the 2:nd test with cap sens. emulsion after 35 min. and 40 sec.


The temperature at the temperature sensor T3 (in the outlet pipe) started to increase after about 34 min. and 40 sec. The temperature fluctuated up and down and finally after 70 seconds ended in a detonation.


9638G

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