Perhaps no other problem (except fire or explosion) has the potential for degrading ESP
performance as much as hopper pluggage. Hopper pluggage can permanently damage an
ESP and severely affect both short-term and long-term performance. Hopper pluggage is difficult to diagnose because its effect is not immediately apparent on the T-R set panel
meters. Depending on its location, a hopper can usually be filled in 4 to 24 hours. In many
cases, the effect of pluggage does not show up on the electrical readings until the hopper is
nearly full.
The electrical reaction to most plugged hoppers is the same as that for internal misalignment,
a loose wire in the ESP, or excessive dust buildup on the plates. Typical symptoms
include heavy or "bursty" sparking in the field(s) over the plugged hopper and reduced
voltage and current in response to the reduced clearance and higher spark rate. In
weighted-wire designs, high dust levels in the hopper may raise the weight and cause slack
wires and increased arcing within the ESP. In many cases, this will trip the T-R set off-line
because of overcurrent or undervoltage protection circuits. In some situations, the sparking
continues even as the dust level exceeds hopper capacity and builds up between the
plate and the wire; whereas in others, the voltage continues to decrease as the current
increases and little or no sparking occurs. This drain of power away from corona generation
renders the field performance virtually useless. The flow of current also can cause the
formation of a dust clinker (solidified dust) resulting from the heating of the dust between
the wire and plate.
The buildup of dust under and into the collection area can cause the plate or discharge
electrode guide frames to shift. The buildup can also place these frames under enough
pressure to distort them or to cause permanent warping of the collection plate(s). If this
happens, performance of the affected field remains diminished by misalignment, even
after the hopper is cleared.
Hopper pluggage can be caused by the following:
• Obstructions due to fallen wires and/or bottle weights
• Inadequately sized solids-removal equipment
• Use of hoppers for dust storage
• Inadequate insulation and hopper heating
• Air inleakage through access doors
Most dusts flow best when they are hot, therefore, cooling the dusts can promote a hopper
pluggage problem.
Hopper pluggage can begin and perpetuate a cycle of failure in the ESP. For example,
there was a case where a severely plugged hopper misaligned both the plates and the wire
guide grid in one of the ESP fields. Because the performance of this field had decreased,
the ESP was taken off-line and the hopper was cleared. But no one noticed the deteriorated
condition of the wire-guide grid. The misalignment had caused the wires and weight
hooks to rub the lower guide and erode the metal. When the ESP was brought back online,
the guide-grid metal eventually wore through. Hopper pluggage increased as weights
(and sometimes wires) fell into the hopper, plugging the discharge opening and causing
the hopper to fill again and cause more misalignment. The rate of failure continued to
increase until it was almost an everyday occurrence. This problem, which has occurred
more than once in different applications, demonstrates how one relatively simple problem
can lead to more complicated and costly ones.
In most pyramid-shaped hoppers, the rate of buildup lessens as the hopper is filled due to
the geometry of the inverted pyramid. Hopper level indicators or alarms should provide some margin of safety so that plant personnel can respond before the hopper is filled.
When the dust layer rises to a level where it interferes with the electrical characteristics of
the field, less dust is collected and the collection efficiency is reduced. Also, reentrainment
of the dust from the hopper can limit how high into the field the dust can go. Although
buildups as deep as 4 feet have been observed, they usually are limited to 12 - 18 inches
above the bottom of the plates.
performance as much as hopper pluggage. Hopper pluggage can permanently damage an
ESP and severely affect both short-term and long-term performance. Hopper pluggage is difficult to diagnose because its effect is not immediately apparent on the T-R set panel
meters. Depending on its location, a hopper can usually be filled in 4 to 24 hours. In many
cases, the effect of pluggage does not show up on the electrical readings until the hopper is
nearly full.
The electrical reaction to most plugged hoppers is the same as that for internal misalignment,
a loose wire in the ESP, or excessive dust buildup on the plates. Typical symptoms
include heavy or "bursty" sparking in the field(s) over the plugged hopper and reduced
voltage and current in response to the reduced clearance and higher spark rate. In
weighted-wire designs, high dust levels in the hopper may raise the weight and cause slack
wires and increased arcing within the ESP. In many cases, this will trip the T-R set off-line
because of overcurrent or undervoltage protection circuits. In some situations, the sparking
continues even as the dust level exceeds hopper capacity and builds up between the
plate and the wire; whereas in others, the voltage continues to decrease as the current
increases and little or no sparking occurs. This drain of power away from corona generation
renders the field performance virtually useless. The flow of current also can cause the
formation of a dust clinker (solidified dust) resulting from the heating of the dust between
the wire and plate.
The buildup of dust under and into the collection area can cause the plate or discharge
electrode guide frames to shift. The buildup can also place these frames under enough
pressure to distort them or to cause permanent warping of the collection plate(s). If this
happens, performance of the affected field remains diminished by misalignment, even
after the hopper is cleared.
Hopper pluggage can be caused by the following:
• Obstructions due to fallen wires and/or bottle weights
• Inadequately sized solids-removal equipment
• Use of hoppers for dust storage
• Inadequate insulation and hopper heating
• Air inleakage through access doors
Most dusts flow best when they are hot, therefore, cooling the dusts can promote a hopper
pluggage problem.
Hopper pluggage can begin and perpetuate a cycle of failure in the ESP. For example,
there was a case where a severely plugged hopper misaligned both the plates and the wire
guide grid in one of the ESP fields. Because the performance of this field had decreased,
the ESP was taken off-line and the hopper was cleared. But no one noticed the deteriorated
condition of the wire-guide grid. The misalignment had caused the wires and weight
hooks to rub the lower guide and erode the metal. When the ESP was brought back online,
the guide-grid metal eventually wore through. Hopper pluggage increased as weights
(and sometimes wires) fell into the hopper, plugging the discharge opening and causing
the hopper to fill again and cause more misalignment. The rate of failure continued to
increase until it was almost an everyday occurrence. This problem, which has occurred
more than once in different applications, demonstrates how one relatively simple problem
can lead to more complicated and costly ones.
In most pyramid-shaped hoppers, the rate of buildup lessens as the hopper is filled due to
the geometry of the inverted pyramid. Hopper level indicators or alarms should provide some margin of safety so that plant personnel can respond before the hopper is filled.
When the dust layer rises to a level where it interferes with the electrical characteristics of
the field, less dust is collected and the collection efficiency is reduced. Also, reentrainment
of the dust from the hopper can limit how high into the field the dust can go. Although
buildups as deep as 4 feet have been observed, they usually are limited to 12 - 18 inches
above the bottom of the plates.
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