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Articles


05.08.2009

Power efficient operation of pumping equipment

In recent years the matters of effective work of the pump-and-power equipment have turned in increasingly pressing problems because of rise in electricity prices; running costs for electricity within the scope of full costs can be very heavy.
Authors :
I.B.Tverdokhleb, Doctor of Engineering, HMS Group Management Company R&D Director
A.V. Kostyuk, Doctor of Physics & Mathematics, HMS Group Management Company Programme Director

Water-supply and water-drain are related to productive industries with intensive use of the pumping equipment, the rate of electric power consumed by pumps makes up more than 50% of the total energy consumption. Therefore the cost reduction in energy consumption for the water supplying organizations is under consideration more than anything else and boils down to effective use of pumping equipment.

Efficient practice work towards energy saving is carried out by HMS group - the holding company which unites leading manufacturers of pumping equipment in Russia and the CIS. At present the company's structure includes 16 enterprises with total number of the personnel more than 12 000 workers. Namely, the widely reputed machine building enterprises Livnynasos, Livgidromash, Nasosenergomash, Bavlenskiy zavod Electrodvigatel , Zavod Bromburvod and soon.

On the average the efficiency factor of the pumping stations amounts to 10-40 %. In spite of the fact that the efficiency of the most often used pumps makes up 60% minimum just for the pumps of К and КМ types and more than 75% for D pumps.

Major reasons of inefficient use of the pump equipment are the following ones:

  • Parameter overriding, i.e. adjusting the pumps for greater capacity and head than it is required for ensuring operation of the pump system.
  • Adjustment of operating mode of the pump by the use of gate valves.

Major reasons of pumps' parameter overriding are the following ones:

  • In the design phase the pumping equipment is build with supposed reserves in case of unforeseen peak loads or with allowance for perspective growth of the service area, manufacturing work and so on. Cases when the similar reserve coefficient can arrive at 50% are frequent.
  • Change of work process-related parameters – deviations from project documentation during building work, corrosion of pipes during operation, replacement of pipeline sections during repair actions, etc. Change in amount of water consumed in connection with population upsurge or decline, change of number of the industrial enterprises and so on.

All these factors results in non-compliance of parameters specified at the pumping stations to the requirements of the system. To ensure correct parameters of the pumping stations for capacity and head within the system the maintaining organizations resort to the flow control with the help of gate valves: thus arriving at substantial increase of power consumption as because of operation of the pump with low efficiency and by reason of throttling losses.

As a rule the Consumer wrongly attributes too low energy efficiency of the system «pump-power network» to low efficiency of the pump, but as the pumps of Russian production principally are operated at water-supply sites, so the public opinion about unreliability and low efficiency of domestic pump manufacture is developed. In addition to low coefficient of efficiency the operation of the pump outside the limits of the operating range considerably reduces their lifetime and reliability.

In case of replacement of the pump equipment the main purpose is defined as actual reduction in energy consumption.

The representatives of foreign companies giving proof of first application of foreign equipment perform a comparative analysis by using initial information on pumps' energy consumption under field conditions and compare with official data of catalogues of foreign producers. As a result of such data analysis the hasty conclusion about supposedly quick payback period of foreign equipment within one-two years is drawn, whereas the cost of foreign equipment exceeds that of the home-made equipment by several times.

The primary reason for considerable reduction of power consumption during replacement of pumps for new ones is not the technical superiority of reinstalled pumps but the compliance of their parameters with the system requirements.

The said compliance is reached by correct selection of the pump according to real characteristics of the system. Therefore the comparative data which are offered in open sources of information and advertising materials about power efficient replacement of pumps of Russian production by pumps of foreign production showing 20-30 % of energy saving are incorrect. Water-supply systems which process quality parameters are time-spaced according to change of daily or seasonal water consumption are not easy to be completed with the pump which operating range would cover the system parameters' size of changing. In this case significant saving may be obtained through application of control systems for the pump installations in dependence on changing parameters of the networking equipment. In such systems the regulation of pumps' parameters is carried out by means of frequency & cascade control.

According to Hydraulic Institute of the USA and European association of pump manufacturers the main activities which can result in reduction of energy consumption and its rates are the following ones, as specified in the Table.

Reduction in energy consumption
within the pumping systems. Generalized methods
Rate of reduction
in energy consumption
Change of feed control by using gate valve for feed control through the instrumentality of the frequency converter
10 – 60%
Speed reduction 5 – 40%
Cascade control by way of parallel installation of the pumps 10 – 30%
Cutting of the impeller, replacement of the impeller 10 – 20%
Replacement of the electric motors by more effective ones  1 – 3%
Replacement of the pumps by more effective ones
1 – 2%


Bear in mind that reduction in energy consumption because of replacement of the pumps by similar machines will effect a saving of 2%. The prime potential relating to energy savings involves change of feed control of the pump by using the gate valve for the current frequency & cascade control; namely, application of the systems capable of conforming the pump parameters to the requirements of the system.

When making a decision on use of either method of control one should consider that every one of the control methods is to be applied with allowance for networkwide parameters for which the pump is operated, in particular, the level of static and dynamic components.

As is evident from the first diagram shown in Figure1, when the pump is networked with dominating static component the drop of the pump revolutions up to 83% from the nominal value results in loss of efficiency with 60 up to 35% and going out of the working point outside the operating range. Therefore in case of networkwide operation of the pump with dominating static component the application of the frequency drive is regarded as unreasonable feature and it must be analyzed more carefully.

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Fig.1. Operation of the pump with networkwide frequency control with dominating static component .

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Fig.2. Operation of the pump with networkwide frequency control with principal losses on friction.

On the other hand, networkwide operation of the same pump for different rotational speed and with principal losses on friction, Figure 2, leads the working point to move along the line of maximum efficiency, and the pump works under optimum condition at all frequencies. Therefore the application of the frequency drive for the pumps operating within the systems with principal losses on friction is regarded as the most efficient practice: thus providing significant reduction of energy consumption.

As is evident from the diagrams shown in Figure 3, when the cascade control is applied to operation of the pumping station by way of switching on/off the necessary quantity of pumps mounted in parallel for networkwide operation and with dominating static component, the summarized pump delivery is on the increase by about the same value.


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Fig.3. Cascade control for networkwide operation of the pumping station with dominating static component.

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Fig.4. Cascade control for networkwide operation of the pumping station with dominating dynamic component.

During networkwide operation of the same pumping station with principal losses on friction, Fig. 4, the network connection of next following pump leads to disproportional increase in summarized delivery. Moreover, the connecting up of every following pump increases the delivery to a lesser extent.

In this regard, practical use of the cascade control is efficient within the systems with dominating static component, but the use of frequency control is recommended for the systems with principal losses on friction.

Conclusions. At the present time there is a widespread myth that energy saving on replacement of home-produced pumps for import pumps might run up to 20-30%. The facts related in the article indicate that power efficient operation of the pump is ensured, essentially, by matched network operation.

Parameters of the pumps fabricated by HMS Group, as far as the efficiency and power consumption are concerned, are not worse than pumps of import production, but at times they are higher-ranking. When the power consumption of similar pumps produced by different manufacturers is compared, it is necessary to pay attention to equality of capacity & head parameters for which the pump is to be selected.

Significant reduction in energy consumption of pumping stations can be achieved by using pumping equipment of home manufacture but at considerably small expenses.