2.8.2 .Jet Pumps

4 Nos. Jet pump shall be supplied per unit. A jet pump should comprise an inlet section, a high pressure water supply connec­tion through a converging nozzle, a mixing zone and a diverging discharge section to the slurry pipe system.

                        The design of the Jet pump shall allow for the easy and quick inspection, removal and replacement of the jet pump sections that are subject to wear.  This applies in particular to the pump throat and the high pressure water nozzle.  The throat shall be considered as that segment of the jet pump, which is between the inlet section and divergent section of the jet pump and is having the least diameter.

                        Jet pump shall be constructed from suitable hard and abrasion resistant materials.

                        The jet pumps shall be designed to meet the requirement specified and Jet pump shall be designed so that it will convey ash at the rated capacity with a minimum of 25 mm wear on the diameter of the throat. The material of construction of the jet pump shall be :

                        Inlet Suction                  Alloy Steel

                        Discharge Tail Piece      IS:4771, Type 1A, Min. 4.5% Nickle with hardness of 500 BHN

                        Nozzle Inlet                   CI Gr. FG-260 as per IS-210

                        Nozzle tip                     Ceramic lined SS/Tungsten Carbide.

8.3 Slurry Line Valves

                        Adequately sized motor operated or solenoid operated pneumatically actuated metal to metal seated knife edge gate valves/100% tight shut off rubber lined knife edge gate valves/plug valves shall be provided at the outlet of Jet pumps handling bottom ash at the suction and at the suction and discharge of combined ash slurry disposal pumps and BA over flow water pumps. 

                        The selection of the type of valve shall be done based on the line pressures.

                        It shall be ensured that the metal to metal seated knife edge gate valves strictly meet the testing requirements of MSS-SP 81 code for seat leakages.  No deviation shall be permitted from the acceptability norms of seat leakages as highlighted in the above referred code.  Bidder shall ensure that offered design of metal to metal seated knife edge gate valve is proven.  The rubber seated knife edge gates valves shall have 100% tight shut-off in both the directions of flow. 

                        Valves shall be provided with a mechanical indicator and limit switches to indicate open or closed position of the valve locally and remotely. 

                        Valves shall be provided with handwheel for manual operation. Gear operator of proven quality and reputed make shall also be provided if the effort required to operate the valve exceeds 25 Kgf. 

                        Valves shall be specially designed for tough, abrasive and corrosive services. 

                        End to end dimensions of plug valves shall be in accordance with ANSI B-16.10 or as per codes to which they conform to. 

As the accumulation of solid material in seat area could affect the tight closure of the valve (which may lead to premature wear due to improper shut off or the gate remaining partially in the flow path) and the wear of seat, deflection cone/wear liner (of minimum 400-450 BHN hardness) to limit such occurrences shall be provided. 

                        The valves shall be selected as follows:

 (i)               For working pressure upto 10 kg/cm² — Metal to metal seated knife gate valve or 100% tight shut off rubber lined knife edge gate valve shall be selected.

(ii)              For working pressure above 10 kg/cm² – Plug type regular pattern valve or 100% tight shut off rubber lined knife edge gate valve shall be used.

(iii)            Size of valves shall be same as parent pipe size.

(iv)            Valves shall be motor/solenoid/pneumatic actuated with provision of handwheel for manual operation. 

                        Material of construction shall be as follows: 

                        Body/Cover      –   Cast iron FG-260 to IS:210 (min. 10 mm thickness) with alloy C.I./S.S deflection cone (minimum 400 BHN hardness) for knife edge gate valves.                                                       OR

                                                     Carbon steel to ASTM – A – 216 Gr. WCB (0.3% carbon max.) for plug valves. 

                        Gate/Plug        –   Stainless steel with min. 400 BHN Hardness on wear surface       for knife edge gate valves                                                             OR

                                                     Carbon steel to ASTM-A-216 Gr. WCB with hardness of 400-450 BHN suitably impregnated for low friction. 

                        Stem                 –    Stainless steel (SS-316) for knife edge gate valves

                                                                                    OR

                                                      IS:1875 Class C made out of ASTM-A-105 (forged carbon steel) and will be suitably impregnated for low friction. 

                        Sleeve/Yoke      –   Bronze 

                        Gland Packing    –   To suit service requirements

2.8.4. Clinker Grinders

Clinker Grinders

 Clinker grinders shall be of double roll construction suitable for continuous operation and designed to reduce lump size to a suitable dimensions in order to facilitate pumping through the proposed slurry pipe lines. The clinker grinder rolls shall be suitable for rotation in both the directions. Wear plates shall be provided on clinker grinder inlet and other wearing surfaces of the grinder chamber. The bearings of clinker grinders shall be protected from ash particles and shall be grease lubricated, heavy duty, roller bearings. Water sealing arrangement shall be provided at gland seals using clear water turbidity not exceeding 30 to 40 ppm. The clinker grinder shall take its drive from a motor through a gear drive. The drive for the clinker grinder shall be transmitted from the motor through a fluid coupling to the gear drive to protect the motor against excessive torque should the rolls stall or jam. One of the rolls of clinker grinder shall receive the drive from the prime mover while the other roll shall be idler type driven through a gear arrangement from the first roll. The clinker grinder speed shall not exceed 40 rpm and the grinder drive motor speed shall not exceed 1000 rpm. The clinker grinders shall be provided with a reversing mechanism to reverse the direction of the grinder rolls should an obstruction stall the grinder. Reversible drive motors shall be amply sized for frequent start-stop-reverse-stop and start duty which may occur several times the quick succession during grinder operation. Common steel fabricated based frame for grinder motor and drive shall be furnished. Grinder drive shall be so interlocked that the motor does not start till sufficient pressure is obtained in its seal water connections. Other interlocks as required for safe and reliable operations shall also be provided.

 Material of construction shall be

(a) Grinder Chamber Carbon Steel (IS:226) 10 mm thick.

 (b) Wear Plates 12-14% Mn. Austenitic steel plates to IS:276, 10 mm thick

(c) Grinder Rolls & teeth Hadfield’s Manganese steel (ASTM A128, 12-14% Mn) casting shop hardened to 300-BHN at all working surfaces and work hardened to 400 BHN at site.

 (d) Grinder shaft Stainless Steel 304/EN-8. (e) Shaft sleeve Hardened stainless steel 410/416 (f) Clinker outlet chute 10mm thk mild steel (IS:226) lined with wear resistant liners as above.