Paper Technology International 2024 - Journal - Page 99
PAPERTECHNOLOGYINTERNATIONAL
e昀케ciency:
OOptimizing
Understanding and harnessing the
potential of Thermocompressors
to minimize waste
Steve Letwin, Specialist – Steam and Condensate Systems – Deublin Company
Alos Almeida, Global Market Manager Paper & Corrugating, Deublin Company
INTRODUCTION:
Thermocompressors are widely used in numerous paper mills, primarily for recompressing and recycling blow-through steam in
dryer drainage systems. Requiring minimal maintenance and utilizing both kinetic and heat energy from the motive steam, they are ideally
suited for this application. However, in practice, there are considerable questions regarding the design and application of these devices.
As machines become more ef昀椀cient, i.e. operating with lower blow-through and differential pressure across the dryers (DP), a
signi昀椀cant number of improperly sized thermocompressors are observed in the market. This inadequacy compromises potential savings
and machine ef昀椀ciencies. In a recent machine upgrade, for instance, six existing thermocompressors lacked suf昀椀cient turndown capacity
to accommodate the new conditions. They were oversized and likely worn out, resulting in compromised performance, and decreased peak
ef昀椀ciency. By replacing all six thermocompressors, the paper mill managed to save up to 11,400 kg/h of motive steam, achieving a return on
investment in less than six months.
Additionally, there are also cases where customers are trying to utilize thermocompressors to control DP, which prevents
ef昀椀cient operation of most dryer sections at low pressures, produces huge steam losses on breaks and loss of control, and contributes to
frequent 昀氀ooding of dryers. For example, we found that a large paper machine producing containerboard grades running DP control with
thermocompressors was having signi昀椀cant 昀氀ooding events, which compromised production and lowered the reliability of the whole dryer
drainage system.
As demonstrated in the cases above, and considering the increasing focus of paper mills on enhancing ef昀椀ciencies, there is a
pressing need to gain a deeper understanding of the utilization and sizing of this component. By identifying and rectifying inef昀椀ciencies,
mills can substantially enhance their operation ef昀椀ciencies, capacity, and 昀椀nancial returns.
Figure 1: Thermocompressors belong to the family of
ejectors, or jet pumps, but instead of rotating parts, they
use a high-pressure motive 昀氀uid to do work on a lowpressure suction 昀氀uid. They are very simple in construction.
The mechanics
Thermocompressors belong to the family of ejectors, or
jet pumps, but instead of rotating parts, they use a high-pressure
motive 昀氀uid to do work on a low-pressure suction 昀氀uid. They are
very simple in construction (Figure 1:). Essentially, it is a pipe elbow
with a steam nozzle directed down the long leg. A check valve is
required in the inlet approach piping to prevent back 昀氀ow in case
the steam jet is shut off. It is important to keep in mind the following
key aspects of thermocompressors: (1) location and length of the
throat; (2) the length and taper angle of the tail piece, and (3) the
shape of the steam nozzle. Motive steam 昀氀ow is controlled by a
tapered needle in the nozzle, effectively a variable ori昀椀ce rather
than a pressure reducing valve. In principle, when the spindle
is opened, high pressure motive steam expands at high velocity
through the nozzle, the jet exiting from the nozzle entrains suction
low-pressure steam which accelerates into high velocity in the throat
of the thermocompressor. The resulting mixture recovers pressure
as it decelerates in the tapered tail piece, being discharged at an
intermediate pressure. Thus, the energy of high-pressure steam is
utilized to-compress low pressure steam to a higher pressure, i.e., a
steam jet compressor.
One key mistake made by end users is to treat them as
“off-the-shelf” items. It is crucial to understand that the design of
thermocompressors involve customizing them to a range of machine
conditions and operation. The use of the speci昀椀ed conditions will
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