Case histories: horizontal pumps

Self-priming horizontal pump for chemical plant

The initial problem

The need arose in chemical plants for an emergency pump to drain and transfer different solutions of liquids (predominantly a solution of HCl at ambient temperature) and in any case in continuously changing environmental situations. The pump (necessarily a horizontal centrifugal pump) had to be portable and driven by a combustion engine: in fact the pump was mean to be used in all emergency situations which might take place in a large chemical plant (which also include the possible need to work during an electrical blackout).

The proposed solution

self-priming emergency pump in a chemical plant
A self-priming pump was proposed bare shaft and with oversized support, characterized by the use of a flexible joint for coupling with the diesel engine. PVDF was selected as the pump material (for its high and well known characteristic of chemical resistance  to the acidic agents). The pump, complete with a priming tank, was mounted on a trolley to be more easily towed to wherever it was needed. The pump was carefully assembled to keep the engine base separate from the pump base in order to minimize the any transmission of vibrations between the engine and the pump.

Observations

Previous pumping operations were always performed with a metal pump, with evident and continuous corrosion problems for parts in contact with the liquid. The replacement with a plastic centrifugal pump  (PVDF) has definitively resolved problems related to the deterioration of the instrument, contributing to plant safety equipment efficiency. Pump model: OMA100A (operating point: 10 m³/h @ 40 m w.c.). The pump was also delivered with performance curves with showing flow rate and head at various speeds of rotation: in this way, it was easier to evaluate the volume of liquid transferred simply using a chronometer and a pressure gauge.

Centrifugal pump for a chlorination system

The initial problem

Heavy wear on a series of pumps installed in a pool chlorination system resulted in very frequent maintenance operations (and in some cases replacement operations) for the pumps in use (regenerative pumps). The wear was caused by the presence (impossible to eliminate) of suspended solids in the liquid being pumped (calcium hypochlorite and dichloroisocianurate). This resulted in decaying performance. In addition to the abrasive particles, the customer also had clearance problems and needed to limit the installed power.

The solution proposed

PVC centrifugal pump for pools
Horizontal centrifugal pump with mechanical seal (material of construction: PVC) instead of regenerative pumps. Thanks to the special design of the hydraulic part, a characteristic curve similar to that of a regenerative pump was obtained(high head and low flow rate) and it was also possible to keep the installed power low with the double advantage of limiting the pump dimensions and optimizing energy consumption. During the design phase it was necessary to reconcile the hydraulic efficiency needs with the particular abrasion resistance needs. In particular, it was necessary to guarantee that particles approximately 8 mm in diameter could pass through the pump without causing clogging or abrasion problems in the hydraulic circuit, composed of the casing, the covers and the impeller.

Observations

The old regenerative pumps were replaced while maintaining at the same time very similar performance and specifically: a high head and low flow rate. The pump's limited clearance dimensions facilitated installation within the chlorination system compartments. An OMA30A pump was used (operating point: 30 l/min @ 17 m w.c.).

CENTRIFUGAL PUMP FOR MUNICIPAL WASTEWATER TREATMENT PLANT

The initial problem

A large municipal wastewater treatment plant had the problem of reducing the frequency of maintenance operations which caused long and fastidious shut-downs of the deodorizing process with consequential discomfort for the inhabitants in the areas surrounding the plant. The horizontal pumps used had problems with the seal and with the motor bearings, parts that required frequent changing, with a consequential increase in operating costs.

The solution proposed

Horizontal pump with double mechanical seal
The entire liquid handling system was replaced by adopting new pumps equipped with a double mechanical seal (composed of SiC and PTFE) flushed with water and motors equipped with special bearings, particularly adapted for withstanding axial loads. The pumps were OMA50B model horizontal pumps (operating point: 24 m³/h @ 10 m w.c.) constructed from PP. The double seal allowed the pump life to be lengthened and prevented problems related to the pumping of liquids subject to crystallization (water originating from the scrubber towers). In particular, the customer recorded a 13% reduction in operating costs.

Observations

A double seal is preferable to the "simple" seal whenever:The mechanical seal most widely used one having a tandem assembly flushed with clean water; but in specific cases a "pressurized" mechanical seal can be used or a liquid other than water can be used for flushing.
For example there are cases in which the water is incompatible with the liquid being pumped (ex. danger of exothermic reactions) or cases in which the water is incompatible with atmospheric conditions (ex. installations in surroundings at temperatures far below 0°C). The double seal can also be used to protect the liquid being pumped from possible contamination that could originate from the outside.

PVDF Horizontal centrifugal pump

The initial problem

A metal horizontal pump had continuous problems caused by hydrochloric acid vapors (pumped at high temperature and high pressure in a pharmaceutical plant). Corrosion problems that especially effected the seal.

The proposed solution

Horizontal PVDF OMA pump

A horizontal pump constructed of PVDF and equipped with a PTFE/Ceramic seal (furnished with PFA coated springs) and special FEP coated O-rings. A OMA70 pump was used (operating point: 19 m³/h @ 20 m w.c.).



Observations

The fluoropolymers FEP and PFA, like PTFE, are chemically inert to all chemical agents, to their different concentrations and combinations and to the operating temperatures compatible with materials with which the Barbera pumps were built (45°C = PVC, 90°C = PP, above 100°C = PVDF). Because of these chemical characteristics, they are used for coating O-rings and seal springs.






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