The pumping of liquids with a high dry-solids content is of
great importance for the pulp and paper industry. The MCE™ pump from Sulzer
Pumps achieves a previously unattained level of performance with regard to the
consistency, temperature and pressure of the pumped medium, as well as to the
efficiency of the pumping system.
The manufacture of pulp and paper entails the pumping of
stock in numerous process stages. Sulzer Pumps in Finland supplies MC® medium
consistency pumps and other MC® equipment which can handle stock with
consistencies of up to 18%. When stagnant, stock with such a high consistency
is so solid that it would be possible to stand on it without sinking in.
This stock has to be fluidized in order to be pumped. This
means that the fiber network has to be disrupted so that the stock begins to
flow like water. For maximum efficiency, air present in the pulp and paper
industry, this is realized with the aid of a specially designed impeller and
pump hydraulics.
MC® pumping and chemical mixing systems are the most
important stock transfer equipment in the modern O2 delignification
and bleaching processes, in recycled fiber and mechanical pulp lines.
Third generation of
MC® pumps.
The first commercial centrifugal medium consistency (MC®)
pump in the world incorporating degassing was delivered by Sulzer Pumps Finland
and started in a Finnish chemical pulp bleaching application in 1980. Since
then, a third generation, MCE™, has been introduced into the market with
deliveries already into three figures. MCE is designed for larger capacity
ranges, higher pumping heads, higher consistencies and significantly lower
energy consumption.
With the MCE™ pump, a new level of performance over a wide
consistency, temperature and pressure range is provided by the Fluider™
impeller. It incorporates effective multi-functional turbulence generation, gas
separation, pumping hydraulics and degassing combined with a wide-passage gas
removal system of high capacity. MCE™ pumping system products can deliver
production rates of 20 to 5000 tpd, a head range of up to 720 feet, as well as
what is considered to be the highest efficiency on the market.
Three degassing
alternatives
The new MCE™ pump products guarantee that a high-performance
pump is available for most of the prevailing pumping conditions and
applications, also giving optimum reliability and inter-changeability with
existing pumps. It is provided with a separate external MDS degassing system or
with a built-in degassing system. Both these alternatives have a high-capacity
vacuum pump running with or in the MCE™ pump. The Fluider™ impeller with MCE™
hydraulic design has made it possible to provide a new, third type of effective
degassing without the use of a vacuum pump. This is an effective solution for a
wide range of applications removing sensitive components and extra controls or
drives from the pump.
The new MCE™ pumping performance level has eliminated the
need for parallel pumping and mixing applications in high production bleaching
sequence designs. Furthermore, the retrofit of earlier generations of existing
MC® pumps with MCE™ pumps results in improved process economy and increased
production rate. MCE™ retrofits are possible with only minor mechanical
modifications, often requiring no piping or drive changes.
The pump can typically reach a head increase of 100 feet in
an existing application with the existing drive unit arrangement. This minimal
modification allows for a variety of process improvements, including increased
operating pressure levels, higher consistencies or increased production rates.
Benefits have ranged from lowered operating costs (consumption of chemicals,
steam, energy, etc.) to increased production.
Mills have reported paybacks in as little as 2-3 months. The
most common application of MC® pumping is to pump stock from washers and
thickeners. The stock falls into the drop-leg and then is transferred to the
subsequent process stage by the MCE™ pump. All the stock falling into the
drop-leg can be pumped further at the highest possible consistency and
temperature. As an example: – with the new MCE™ pump innovations, stock with a
consistency of 14-16% and temperature of +203°F can now be pumped from a
low-level pumping vessel. This is a significant saving in process costs (steam)
and an expenditure advantage.
A wide range of other Sulzer MC® pumping process
applications has also become a standard in the pulp and paper industry. These
include tower discharge pumping systems, long distance and high-pressure
booster pumping systems and controlled flow splitting applications.
Research and development receive top priority at Sulzer
Pumps. As a result, the company has several patented inventions and a growing
number of pending applications relating to the MC® technology. At the
full-scale R&D center in Karhula,
Finland, the
equipment is tested and developed under full process conditions.
The company’s foundry in Finland and its comprehensive
metallurgical know-how adds considerable strength in developing equipment for
these applications where special corrosion and wear resistance are often
required.
Sulzer’s experience, process knowledge and commitment to the
pulp and paper industry has made it a leader in stock pumping, transfer and
mixing technology. As the original MC® pump manufacturer it covers the largest
share of running applications globally with more than 2,500 [as of September
2002] delivered MC® pumping systems.
Resala, Reijo. “Medium Consistency MC® pumping
systems.” Paper Equipment & Materials International Sept. 2002:
16-17.