cooling t-Thermal power plantsower

In thermal power projects the circulating water system is most important. The more efficient the system works will keep the power output of the plant in tact. The purpose of providing Circulating water system is for supplying water to the condenser for condensing the LP turbine exhaust steam and also for secondary cooling of boiler and turbine auxiliaries. The circulating water system is normally of two different types. One of them may be once through type in which the system operates without cooling tower and the other type may be closed cycle recirculation type which uses  cooling tower. when cooling water is available in large quantity such as sea water source of water for cooling systems like circulating water systems in  coastal power stations the once through condenser cooling system is used for direct cooling  When plant water is drawn from fresh water sources such as river, canal, lake, and reservoir Closed cycle condenser cooling system using cooling towers is implemented by  the power plants based on fresh water sources to meet their water.. Sea water based cooling towers are also adopted at coastal sites depending upon techno-economic considerations.  Two types of cooling towers are normally used in the power plant. One is mechanical induced draft type cooling tower and the other one is  natural draft type cooling tower. The selection of the cooling tower depends on capital cost and operating expenses and consideration of site specific issues. In general, mechanical induced draft tower are preferred for power plants .The operating expenses of mechanical induced type cooling towers can be optimised when it is constructed very close to pit heads. Natural draft tower are preferred when the power plants are located at load centres (far off from pit head) as these do not involve any rotating equipment, thus saving on costly power. Air flow rate through Natural draft cooling tower depends on the density difference between ambient air and relatively hot & humid light air inside the tower. For sites with

Considerable duration of high summer ambient temperatures coupled with low

Relative humidity values adequate density difference would not be available for

Proper design and operational performance of Natural draft cooling tower . For such sites, mechanical induced draft type cooling towers should be preferred . In case of once through system, desisting arrangement and travelling water screens of appropriate mesh size are provided at the intake section to prevent debris and biological species in source water from entering to cooling water and plant water systems. In case of sea water based cooling water system, debris filters of appropriate mesh size shall be provided at upstream section of condenser for further removing debris from the cooling water and thus reducing fouling of condenser tubes. In the mechanical induced draft type cooling tower is of single or double inlet,cross flow or counter flow type with the fans located on top of the tower. The

natural draft type cooling tower is of counter flow or cross flow type with draft

for air flow through the packing provided by buoyancy effect of hot and humid

air inside the tower shell as compared to outside ambient air. Splash type or film type. However, due to ambient air having high levels of dust, splash type film is preferred for both types of towers Because of high salt concentration; cooling tower drift and salt contamination in the environment are considerations for cooling towers with sea-water makeup. The drift will contain very high (up to 55,000 ppm) concentration of total dissolved solids, hence a sea water cooling tower should not be located close to sensitive equipment to minimize corrosion effect. To avoid long distance drift of high concentration salt water, it is recommended that the distribution system be designed for low-pressure spray nozzles, which will reduce the quantity of water droplets impinging on the drift eliminators. Drift rate is limited to 0.02 to 0.05 percent of the circulation water flow rate.A typical sea-water cooling tower operates at cycle of concentration ranging from 1.3 to 1.5 and size of cooling tower is 5 to 10 percent larger than a similar capacity fresh-water system. This is because sea water, having high salt concentration, lowers the water’s vapour pressure and reduces the evaporative cooling rate by 5 to 8 percent (depending on salt concentration). Approach temperatures used for design of towers must consider the effect salt water has on tower performance. Distribution piping of PVC performs well in salt water service. The fan blades may be of glass reinforced polyester or epoxy coated aluminum.Gear reducers, bearing housings and fan hubs may be made of cast iron provided they are protected with a heavy coating of epoxy enamel. Mechanical equipment supports and welded steel fan hubs should also be protected with a heavy coating of epoxy enamel. Since stainless steel resists salt water very well in areas which are highly aerated, drive shafts and fasteners in the mechanical equipment should be made with type 316 stainless steel.

Model calculation 3 : Direct Manpower calculation Installation of Heavy Tall towers: I explained in my previous posts the details of direct manpower calculation for vessels of lighter weight. The direct manpower calculation and the effort required for erection of heavy tall towers are not simple like normal heat exchanger or small towers. Either bigger capacity cranes of suitable capacity or availability is normally used in such cases. On occasions considering the weight, non availability of higher capacity cranes, economy an alternate arrangement in place of cranes are used for the erection work is used. . This derrick arrangement is called as Gin Pole arrangement. A gin pole (derived from gin, a three-legged lifting device) is a supported pole which uses a pulley or block and tackle on its upper end to lift loads. The lower end is braced or set in a shallow hole and positioned so the upper end lies above the object to be lifted. The pole (also known as a "mast", "boom", and "spar") is secured with three or more guys. These are manipulated to move the load laterally, with up and down controlled by the pulley or block.

The gin pole is considered a form of derrick, called standing derrick or pole derrick, distinguished from sheers (or "shear legs") by having a single boom rather than a two-legged one.Gin poles are also used to raise loads above structures too tall to reach with a crane, as placing an antenna atop a steeple, and to lift segments of a tower atop one-another during erection. When used to create a segmented tower, the gin pole can be detached, raised, and re-attached to the just completed segment in order to lift the next. The process of "jumping" is repeated until the topmost portion of the tower is completed. .In this model calculation my experience in calculating the direct man power was on the basis of using Gin pole or derrick and direct manpower handling the equipment.. This manpower calculation does not include any manpower for operation and supporting activities of the crane movement

The man-hour calculation of the estimator should include the time to be spent by various technicians/Labourers to complete the activity starting from receiving the materials from stores of the owner, loading, transportation of materials from owners stores to contractors storage yard , unloading and storing at contractors storage at site yard, retransportaion to the point of installation if required , surface preparation of foundations along with time required for fabrication/machining of steel shims to be placed below the equipment installation, man-hours required for installation work for accessories or platforms, man-hours required for testing and commissioning, , Also major important factor which involves lot of man-hours is the scaffolding activity. If the equipment to be installed is at lower level or on ground the Man-hours required for scaffolding will be nil. In case if the installation is at an elevation the man hours required for preparation and installation of the scaffoldings are to be considered The normal activities involved in the installation of the Tall towers after receipt of materials at erection sites are preparation of the foundation and bring down the level of the foundation to receive the equipment on top of it with the space available for placing the equipment on top of the foundation. Normally only maximum of 50mm pacer plates are allowed to be placed between the equipment and foundation so that grouting can be taken can effectively. On preparation of foundation check for the condition of the equipment placed on ground on wooden packers.. Tower Installation Hence details provided by me are bare minimum and guide lines for the estimators in indie. The details provided are based on the productivity of the technicians worked then with me and minor fine tuning as per site data’s of the company .and in consultation with the companies site personals more accurate data’s can be decided by estimators Towers ( considering the erection procedure with Gin Pole Derrick arrangement) Slno Detail Weight of equipment up to 100MT Weight of equipment up to 101-200MT Weight of equipment up to 201-300MT Weight of equipment up to 301-400MT 1 Foundation 80hours 80hours 120hours 120hours 2 Installation 2640hours 2960hours 3360hours 3680hours 3 Total 2720hours 3040hours 3480hours 3800hours The above mentioned man-hours calculation does not include the manpower required for receiving the materials from stores up to erection site, activities related to cleaning of equipments, accessory works related with equipment erection work like platform and ladders erection works for the equipment any major scaffolding works,time required for preparation of testing,commissioning,performance guarantee works . The manpower calculation is on the assumption that the equipment will be installed only on the ground.. Based on the above chart let me calculate the man hours required for a Tall Tower weighing 400 MT and installed at ground floor. As per the chart the time consumed for installation of this equipment is only 3800 Man-hours and time required for other activities can be calculated under respective heads and to be added with the basic man-hours. What should be the cost of this 3800 man-hours. It cannot be purely one category like skilled/highly skilled or semiskilled. It is the combination of the technician group engaged in the installation work. Based on the nature of work the category of people are to be divided. in terms of percentages. In this case the highly skilled labourers may not be required much and unskilled workers also will not be required much. So technicians who have capacity to lift and shift the materials may be required more. If we consider total 100% man-hours equals to 128 Man-hours. Out of which Riggers can be considered as 70%( semi skilled) requirement,15% requirement of skilled and remaining 15% manpower will be unskilled to reach total the 100% Skilled Labours -15%.........!5/100*3800 = 570 Man-hours Semi skilled --70%.......70/100*3800 = 2660 Man-hours Unskilled ...........15%........15/100*3800 = 570 Man-hours Cost of installation of the Tower on basic conditions based on the Man hour rates (Minimum wages) of notification by Delhi state Skilled Labours .........(570/8)* 455 = 32,418.75 Semi skilled --- -(2660/8)*414 = 1,37,655 Unskilled Labours..... .(570/8)*374 = 26647.5 Total cost of Man-hours for Erection of 400 MT Tower on Ground using Gin pole arrangement is Indian rupees at the location near Delhi and at this point of time Hence Rate per MT in that location is Indian Rupees 394.21

Model-02 : Calculation of ditect Man-Hour

This page is in continuation to my earlier post Model-01 : Calculation of ditect Man-Hour  .  The direct manpower calculation and the effort required for erection of different types of vessels varies based on their location of installation, type of handling equipment required for the installation of the equipment. Certain equipments can be erected by manual labour by shifting and placing it on top of the foundation. ( In India manpower availability is plenty and cheap and in most of the construction sites direct labourers are more used along with less amount of lifting equipments like cranes).In this model calculation my experience in calculating the direct man power was on the basis of using a truck crane  and direct manpower handling the equipment. I have not elaborated here the type and capacity of the crane to be used for tower erection. Since selection of a particular type of crane itself is a vast subject and will be dealt in my other posts.  For installation of any vessel apart selection of a suitable crane  for installation of the equipment, based on the weight and other parameters, an additional crane from trailing end  of the equipment use to support the equipment to make it vertical.. This manpower calculation does not include any manpower for operation and supporting activities of the crane movement

The man-hour calculation of the estimator should include the time to be spent by various technicians/Laborers  to complete the activity starting from receiving the materials from stores of the owner, loading,  transportation of materials from owners stores to contractors storage yard , unloading and storing at contractors  storage at site yard, retransmission to the point of installation if required ,  surface preparation of foundations along with time required for fabrication/machining of steel shims to be placed below the equipment installation, man-hours required  for installation work for accessories or platforms, man-hours required for testing and commissioning,

,                                          Also major important factor which involves lot of man-hours is the scaffolding activity. If the equipment to be installed is at lower level or on ground the Man-hours required for scaffolding will be nil. In case if the installation is at an elevation the man hours required for preparation and installation of the scaffoldings are to be considered

                                           The normal activities involved in the installation of the Tall towers after receipt of materials at erection sites are preparation of the foundation and bring down the level of the foundation to receive the equipment on top of it with the space available for placing the equipment on top of the foundation. Normally only maximum of 50mm pacer plates are allowed to be placed between the equipment and foundation so that grouting can be taken can effectively. On preparation of foundation check for the condition of the equipment placed on ground on wooden packers. Using the marking on the tower for slings position the crane as close as possible to lift the equipment.  

Tower  Installation

The below mentioned details were calculated in one of chemical plant i worked. Hence details provided by me are bare minimum and guide lines for the estimators in indie. The details provided are based on the productivity of the technicians worked then with me and minor fine tuning as per site data’s of the company .and in consultation with the companies site personals more accurate data’s can be decided by estimators

Towers ( considering the erection procedure with truck crane)           

Slno	Detail	Weight of equipment up to 10MT	Weight of equipment up to 11-20MT	Weight of equipment up to 21-30MT	Weight of equipment up to 31-40MT	Weight of equipment above 41MT-100MT
1	Foundation	16hours	24hours	24hours	32hours	48Hours
2	Installation	16hours	24hours	32hours	40hours	80Hours
3	Total	32hours	48hours	56hours	72hours	128Hours

The above mentioned man-hours calculation does not include the manpower required for receiving the materials from stores up to erection site, activities related to cleaning of equipments, accessory works related with equipment erection work like platform and ladders erection works for the equipment any major scaffolding works,time required for preparation of testing,commissioning,performance guarantee works . The manpower calculation is on the assumption that the equipment will be installed only on the ground..

                                           Based on the above chart let me calculate the man hours required for a Tower weighing 80MT and installed at ground floor. As per the chart the time consumed for installation of this equipment is only 128Man-hours and time required for other activities can be calculated under respective heads and to be added with the basic man-hours.

                                           What should be the cost of this 128 man-hours. It cannot be purely one category like skilled/highly skilled or semiskilled. It is the combination of the technician group engaged in the installation work. Based on the nature of work the category of people are to be divided. in terms of percentages. In this case the highly skilled labourers may not be required much and unskilled workers also will not be required much. So technicians who have capacity to lift and shift the materials may be required more. If we consider total 100% man-hours equals to 128 Man-hours. Out of which Riggers can be considered as 70%( semi skilled) requirement,15% requirement of skilled and remaining 15% manpower will be unskilled to reach total the 100%

          Skilled Labours -15%.........!5/100*128  = 19.2 Man-hours

          Semi skilled      --70%.......70/100*128  = 89.6 Man-hours

          Unskilled   ...........15%........15/100*128 = 19.2 Man-hours

Cost of installation of the Tower on basic conditions based on the Man hour rates (Minimum wages) of notification by Delhi state

          Skilled Labours .........(!9.2/8)* 455   = 1092

          Semi skilled ---           -(50.4/8)*414    = 4636.8

          Unskilled Labours..... .(10.8/8)*374   =  897.6

Total cost of Man-hours for Erection of Tower of 80MT on Ground is  Indian rupees 6626.4 at the location near delhi.

Hence Rate per MT in that location is Indian Rupees 82.83

You can find out that man power cost decreases with respect to weight of the tower but while we calculate the other cost involvement for installation of the tower like cost and crane hours and additional indirect man power cost we can arrive at the exact cost per MT of heavy equipments which falls under this catogory