GAS VENTING ASSEMBLY FOR VACUUM TRUCK

CONDUIT D'EVACUATION DE GAZ POUR CAMION A RESERVOIR ASPIRATEUR

English Abstract

An elongate tubular stack is pivotally connected by a swivel elbow with
the vent line leading from a vacuum/blower pump connected with the tank of a
vacuum truck. The stack is positioned to extend alongside the tank. A
hydraulic cylinder assembly is connected to the stack for raising and lowering
it between horizontal transport and vertical venting positions. When the
vacuum truck is taking on crude oil into the tank, H2S-containing gas is
vented
through the raised stack. When the truck is travelling, the stack is lowered
to
the horizontal position.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN
EXCLUSIVE PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS
FOLLOWS:
1. In an assembly for venting gas associated with crude oil contained
in an elongated tank mounted longitudinally on a deck of a vacuum truck, said
truck carrying a vacuum/blower pump and vent line for withdrawing the gas
from the tank and discharging it, the improvement comprising:
an elongated tubular vent stack supported by the deck and located
substantially parallel to and alongside the tank, said stack being movable
between a substantially horizontal transport position and a substantially
vertical venting position, said stack having an outlet;
means for pivotally connecting the stack at its front end with the vent
line so that the stack constitutes an extension of the vent line and may pivot
between the transport and venting positions; and
means, connected between the deck and stack, for mechanically
raising and lowering the outlet of the stack by pivoting the stack between
positions.
2. The improvement as set forth in claim 1 wherein the pivot
connection means comprises a swivel elbow and the stack has a length
greater than one quarter the length of the tank.
7

3. The improvement as set forth in claim 2 wherein the raising and
lowering means comprises a hydraulic cylinder assembly pivotally connected
between the deck and the stack.
4. A method for safely venting gas during loading of a vacuum truck
with oil comprising:
providing a vacuum truck having a deck carrying a tank for conveying
crude oil, a vacuum/blower pump for suctioning crude oil into the tank, a
tubular vent line connected with the tank for discharging gas separated from
the oil, and a tubular vent stack connected with the vent line, the vent stack
having an outlet;
raising the outlet of the vent stack upwardly to a venting position
spaced above the deck, for dispersing the gas harmlessly into the
atmosphere; and
initiating loading of oil into the tank.
8

Description

CA 02239628 1998-06-O1
1 FIELD OF THE INVENTION
2 This invention relates to a pivoting stack used on a vacuum truck to
3 vent sour gas emanating from crude oil being taken on into the truck's tank.
4
BACKGROUND OF THE INVENTION
6 Crude oil is commonly conveyed by truck in oil field operations. For
7 example, in the Lloydminster area of Alberta/Saskatchewan, the crude oil is
8 so viscous that it does not lend itself to conveyance by pipeline to an
9 upgrading facility - hence it is conveyed there by large vacuum trucks.
The crude oil commonly has gas associated with it. This gas breaks
11 out of the oil as it is loaded into the tank and needs to be vented off. In
some
12 cases this vented gas contains H2S. Gas containing H2S is commonly
13 referred to as sour gas.
14 Vented sour gas can be deadly if the concentration of HzS is high
enough.
16 Gaseous H2S has a greater density than air. If released into the
17 atmosphere, it has a tendency to settle and collect close to the ground. As
18 additional gas is vented from the tank over time, the concentration of the
H2S
19 increases and a layer of low lying deadly gas can accumulate.
The vacuum trucks used are normally equipped with:
21 ~ a large elongated tank extending the length of the truck deck, for
22 containing the crude oil;
23 ~ a vacuum/blower pump connected with the tank, for suctioning the
24 crude oil into the truck tank and discharging it out of the tank; and
~ a vent line, leading from the pump, for venting the gas.
2

CA 02239628 2001-08-15
1 ~ a vent line, leading from the pump, for venting the gas.
;? For many years, vacuum truck operators have coped with the H2S
.3 problem by attaching and extending a long hose along the ground away from
~4 the vent line outlet, when loading. The gases are vented to atmosphere at
:5 ground level remote from the truck.
~5 This practice has disadvantages, namely:
'7 ~ It is time-consuming for the trucker to string out and pick up the
.3 hose; and
!3 ~ The H2S still collects at ground level in possibly dangerous
1 n concentration, creating a hazard for an individual who inadvertently
11 walks into it.
1;? It is the objective of them present invention to provide a safer and less
13 time-consuming venting alternative.
1 ~~
1;~ SUMMARY OF THE INVENTION
113 In accordance with a preferred form of the present invention, an
1'7 elongated tubular stack is mounted on the truck deck to extend beside and
in
1.3 parallel with the tank. The stack is pivotally connected with the vent
line from
1!a the tank, preferably by a sE~aled swivel elbow. A cylinder assembly is
21) connected between the deck and stack, for mechanically raising and
lowering
21 the stack. The stack is quite long - it extends at least one quarter the
length
2;? of the tank and typically has a length of about 8 feet.
2:3 By equipping the vacuum truck in this fashion, the stack can be raised
2~t and the gas vented to the atmosphere well above the truck, during loading.
3

CA 02239628 2001-08-15
1 In a test, it was determined that the H2S content at the stack outlet,
2 when the stack was in the horizontal position, was in the order of 300 ppm
as
3 determined by an H2S detector. When the 8 foot long stack was raised to the
~4 substantially vertical venting position and the vacuum/blower pump was
actuated to forcibly discharge the sour gas, it was found that the H2S
detector
~6 was unable to detect H2S within a radius of 250 feet from the truck.
7 Broadly stated, the invention is an improvement in an assembly for
B venting gas associated with crude oil contained in an elongated tank mounted
'9 longitudinally on a deck of a vacuum truck, said truck carrying a
1 ~0 vacuum/blower pump and vent line for withdrawing the gas from the tank
and
11 discharging it through the vent line, the improvement comprising: an
12 elongated tubular vent stack ~;upported by the deck and located
substantially
1:3 parallel to and alongside thE: tank, said stack being movable between a
1~4 substantially horizontal transport position and a substantially vertical
venting
1.5 position, said stack having an outlet; means for pivotally connecting the
stack
1 i3 at its front end with the vent lime so that the stack constitutes an
extension of
1'7 the vent line and may pivot between the transport and venting positions;
and
1 ~3 means, connected between the deck and stack, for mechanically raising and
1!~ lowering the outlet of the stack by pivoting the stack between positions.
20 In a method aspect, the invention comprises: providing a vacuum truck
21 having a deck carrying a tank for conveying crude oil, a vacuum/blower pump
22 for suctioning crude oil into the tank, a tubular vent line connected with
the
23 tank for discharging gas separated from the oil, and a tubular vent stack
2~4 connected with the vent line, the vent stack having an outlet; raising the
outlet
4

CA 02239628 2001-08-15
1 of the vent stack upwardly to a venting position spaced above the deck, for
.2 dispersing the gas harmlessly into the atmosphere; and initiating loading
of oil
3 into the tank.
~4
DESCRIPTION OF THE DRAWING
n Figure 1 is a schematic plan view showing a vacuum truck having a
'7 tank, pump, vent line and pivoting stack assembly;
.B Figure 2 is a plan view showing the swivel elbow, stack and part of the
raising/lowering assembly; and
1n Figure 3 is a side view of the assembly shown in Figure 2.
11
1;2 DESCRIPTION OF THE PREFERRED EMBODIMENT
1.3 Having reference to Figure 1, the invention is used in connection with a
1'4 vacuum truck 1 having a deck 2 carrying an elongated tank 3. (The word
1.5 "deck" is intended to collectively describe the truck frame and the deck
1G mounted on it.) A vacuum/blower pump 4 is connected to the tank 3 for
1'7 suctioning oil into it and discharging air and gas, when required. The
pump 4
1.3 is connected with a vent line Ei for venting the air and gas during
loading. All
1!a of the foregoing is conventional.
21) A conventional swivel elbow 6 is connected between the end of the
2'1 vent line 5 and the front end of the stack 7. The elbow 6 can rotate or
pivot
2;? between a horizontal transport: position and a vertical venting position.
It has
23 an internal seal (not shown) with each of the vent line 5 and stack 7, so
that
2~~ gas cannot leak out.
5

CA 02239628 2001-08-15
1 The vent stack 7 is positioned alongside the tank 3 in the transport
2 position. It typically has a length in the order of 4 - 20 feet.
3 A shaft 10 is rotatably mounted in a pillow block 11 mounted on the
4 deck 2 adjacent the elbow 6. A metal post 12 is attached at its lower end to
the shaft 10, for rotation therewith. A sleeve 13 is slidably mounted on the
6 post 12. The sleeve 13 has a lug 14 which is connected by a pin 15 with a
7 yoke 16 carried by a collar 17. The collar 17 is clamped to the stack 7.
8 A double-acting hydraulic cylinder 20 is pivotally attached at one end
9 by a pin 21 to a bracket 22 mounted to the deck 2. The ram 23 of the
cylinder
1 ~0 20 is pivotally connected by a pin 24 with a lug 25 attached to the shaft
10.
11 The hydraulic cylinder 20 is actuated by the truck hydraulic system (not
1;2 shown) and is suitably controlled by valves (not shown).
13 In operation, the outlet 30 of the stack 7 can be mechanically raised by
1~4 extending the ram 23 which rotates the lug 25, shaft 10 and post 12. The
1.5 stack 7 is therefore moved from the horizontal transport position to the
vertical
1 i3 venting position as the sleeve 13 slides up on the post 12. To lower the
stack
1'7 7, the ram 23 is retracted.
1.3 While the form of the invention described herein constitutes a preferred
1!a embodiment of the invention, it will be understood that the invention is
not
20 limited to this form of apparatus but that various changes may be made
21 therein without departing from the scope of the invention which is defined
in
2:? the claims now following.
6

Representative Drawing