Analysis For Operating Cost Of Split Case Pump For Its Life Cycle

Transcription

1 Analysis For Operating Cost Of Split Case Pump For Its Life Cycle P. S. Bolade 1, S. J. Madki 2 1,2 Department of Mechanical Engineering, Brahamdevdada Mane institute of Technology, Solapur, India Abstract Pumping systems for all services consume an estimated one-fifth of all electricity produced. With the changing industrial scenario, customers are now focusing on energy cost and maintenance cost of the product apart from initial investment cost. Earth s resources are finite and also there is a growing concern that the use of energy can contribute directly or indirectly to environmental pollution. KBL as one of the leading pump manufacturer have shown prime responsibility to implement this technology in order to contribute energy conservation. KBL has used this concept effectively in products and introduced in market. Keywords Life Cycle Cost, Split case pumps, Customer Benefit, Energy. I. INTRODUCTION The determination of Life Cycle Cost (LCC) involves following a methodology to identify and quantify all of the components of LCC equation. When used to compare possible design or overhaul alternatives, the LCC process will allow the most cost effective solution within the limits of the available data. The Life Cycle Cost equation can be stated as: [1] LCC = (C ic + C in + C e + C o + C m + C s + C env + C d ) (i) C ic = Initial cost, purchase price. This would normally equate less than 14% of total LCC C in = Installation and Commissioning cost. This would normally equate less than 9% of total LCC C e =Energy Cost. One of the largest cost element in LCC and may dominate LCC of centrifugal pump. This would normally equate less than 32% of total LCC. C o = This may vary widely depending on complexity and duty of the system. For hazardous duty it may be require daily checks for hazardous emissions etc, with higher operating cost. On other hand fully automated, fully automated system, which in turn will reduce operational cost. C m =Maintenance Cost. The design of pump can influence these costs thru the material of construction, design features and ease of assembly / disassembly e.g. back pull out design feature, axially split casing pumps etc C s =Down time and Loss of Production Cost. Despite the design or target life of the pump and its components, there will be occasions when an unexpected failure occurs C env =Environmental Cost. Environmental contamination includes cooling water and stuffing box leakage disposal, contaminated used parts such as seals etc. Cost for environmental inspection should also be included. C d = Disposal Cost. Costs of final disposal and restoration of the local environment must be evaluated to assess the true overall costs of the pumping systems. 1.1Need of life cycle cost analysis and LLC products: Earlier many organizations only consider the Initial purchase and installation cost of the equipment. But in today s competitive market organizations continuously seek cost saving which will improve their profitability. LCC analysis is an effective tool for evaluation of energy coast as well as initial cost. LLC products helps in conservation of energy by maintaining the overall efficiency of the product over the years as compare to conventional products where efficiency depreciation is major concern. The developed world has become acutely aware of the effect of its energy waste and the introduction of levies on CO2 emissions now directly taxes the inefficient users of energy. II. KBL LLC HORIZONTAL SPLIT CASE PUMPS KBL have developed various existing split case models into LLC range having moderate range of flow which is generally required for utility application. Features adopted in the LLC pump: 581

2 1. Double volute casings: Double volute casing reduces radial load and subsequent shaft deflection. This feature is only incorporated where necessary, as double volute design tends to have an efficiency penalty. [5] Fig Impeller Fig Single and Double Volute Casing Customer Benefit: Enhanced bearing life. 2. Coating: The main source of hydraulic loss in the casing is due to the friction losses, so the friction loss is reduced by corrocoating the casing with fluiglide material. Due to flu glide coating the frictional losses in the hydraulic passages of casing is reduced drastically. The surface roughness value of fluiglide coating is lowest as compared to other. [5] Customer Benefit: Reduced energy consumption/cost. Customer Benefit: Increased component life, increased cavitations resistance, Superior hydraulic performance, increased bearing and component life. Overall result in reduced maintenance costs. 4. Shaft: Corrosion resistant rigid stainless steel shaft is standard scope of supply. Low L3/D4 ratio ensures minimum deflection and long bearing life. Maintain optimum efficiency longer, as no contact between impeller and wear rings. [5]. Fig Corrocoating of Volute Casing 3.Impeller: Precision casting in austenitic stainless steel is standard scope of supply. Axially hydraulic balance of double suction design improves efficiency and enhances bearing life. Rotating assemblies are dynamically balanced minimizing vibration. [5]. Fig LLC UP300/46 Pump Shaft: A1120mm, B90mm Customer Benefit: Increased bearing and shaft life. Reduced maintenance and energy costs. 5. Bearings: API type double row angular contact bearing assembly is used. Bearing assembly situated at drive end, ensuring any thermal growth on high temperature service is not transmitted to coupling and driver [5]. 582

3 Fig Double row angular contact bearing Customer Benefit: L10 life in excess of 50,000 hours, under all design load condition. 6. Wear Rings: Wear rings isolate the suction and delivery portions of the casing. As the clearance between the wear ring and impeller increases, water starts flowing from delivery volute to suction chamber. Finally it results in loss of efficiency. LLC impellers are designed with close clearance having labyrinth design. This traps the water flowing from delivery to suction. [5] Fig Mechanical Seal Customer Benefit: Customer Benefit: Zero leakage, low friction, ease of removal. 8. Spacer type coupling along with detachable bearing housing: LLC pumps are supplied with spacer type coupling, Detachable bearing housing i.e. insert and bearing housing are separate and cartridge mechanical seal. [5]. Fig Wear ring O ring is provided between casing and wear ring to avoid leakage through stationary parts. Customer Benefit: Increased component life. Enhanced hydraulic efficiency. 7. Mechanical Seal:- Cartridge type mechanical seal is standard scope of supply. Fig Spacer type coupling 583

4 Customer Benefit: Lower maintenance costs. Improved reliability with reducing downtime and associated costs. 9. Throttle Bush: Throttle Bush reduces energy consumption and facilitates suction lift with single mechanical seals. Fig Throttle Bush Customer Benefit: Low energy costs, also gives intermediate support to shaft results in arresting the shaft deflection and rubbing of wear ring and impeller is avoided. III. THEORITICAL APPROACH TOWARDS EFFICIENCY SUSTAINABILITY IN LLC PUMPS As explained above various features incorporated in KBL LLC pumps results in arresting the deflection of shaft. As there is no rubbing between the wear rings (stationary part) and impeller (rotating part) clearances is maintained as it is. It gives advantage of maintaining the efficiency of the pump over the years. As per HIS - There will be reduction in efficiency by 1.5 to 2.3% if clearance between wear ring increases by 1.5 times of standard clearance and by 2-6 % for increase in wear ring clearance by 2 times than standard. From the reference document of HIS it seems that deterioration in efficiency for conventional pumps will be 1% to 3% for the range of specific speed for which we are developing LLC range pumps. 3.1 Life Cycle Cost Comparison of old Split Case pump and New LLC Split Case Pump: Energy saving by LLC pump can be explained by taking example of one of the developed pump UP300/46LLC.This pump is developed by incorporating all the parameters mentioned in article 2.0 When LLC developed model is compared with the regular pump manufactured in conventional way gives operating cost analysis as below. Running Cost Comparison: [3].Both the pumps are operating at Best Efficiency Point (BEP) 1725m3/hr and 57.5m head at 1450rpm. While regular pump is installed it will give maximum efficiency 88% as per the tested graph. Motor efficiency is 95.5%.Overall efficiency will be 84.4%. Figure 88% is considered without taking effect of acceptable negative tolerance specified in IS9137 otherwise this efficiency will be further reduced in conventional pumps. While LLC pump is installed with corrocoating and incorporating all the features explained in article 2.0, it will give guaranteed efficiency 90%.Also motor used is EFF1 type having 0.5% efficiency higher as compare to regular motor. Motor efficiency will be 96%.Overall efficiency will be 86.4%. Analysis of energy consumption for the first year considering the continuous duty will be as below 584

5 Table1 Above analysis shows how the effect of efficiency depreciation and frictional losses affects the operating cost of regular pump. Operating cost is reduced in LLC pumps as efficiency of the pump is maintained over the years. As maintenance down time is reduced due to added features as explained in article 2.0, maintenance cost is also reduced in case of LLC pumps. Considering % Overall Efficiency Depreciation Rate per year for regular pump analysis of energy consumption for the second year considering the continuous duty will be as follows Table 2 IV. CONCLUSION Customer attitude towards the product is now changing. Earlier his interest was only in initial investment cost and not bothered about operating cost. Now he is thinking from Overall cost of the product which includes initial cost as well as operating cost. Though LLC pumps have initial cost higher in few thousands as compare to regular pumps but energy saving in only three years is in millions. Life Cycle Cost is a highly practical tool for the users which can be very effectively used to evaluate and compare any equipment, particularly for complex pumping systems to make purchase decision from the available alternatives and safeguard own interests. REFERENCES [1 ] Hydraulic Institute and Euro-pump Pump Life Cycle Costs: A Guide to LLC Analysis for Pumping. Systems. Parsippany, N.J.: Hydraulic Institute. [2 ] Bower, John Reducing Life Cycle Cost by Energy Saving in pump systems. In Proceeding. From 1999 Industrial Energy Technology Conference. May.Houston, Tex.: Texas A&M University. [3 ] Barringer, H.Paul A Life Cycle Cost Summery, Barringer & Associates, Inc. Humble, Texas USA(2003). [4 ] US Department of Energy.1999.Improving Pumping System Performance: A Sourcebook for Industry. Washington, D.C.; U.S.Department of Energy, office of Industrial Technologies. [5 ] Double Suction Split Case pumps Horizontally and Vertically Mounted by Grundfos Management. A/S. 585