2.8.16 Air Compressors for Pneumatic Conveying of Ash
Air compressors shall be designed for continuous operation with high efficiency to satisfy the system requirements. Satisfactory operation in parallel shall be ensured without any uneven load sharing, undue vibration, noise etc.
The design shall incorporate every reasonable precaution for the safety of all operation and maintenance personnel. Each compressor unit should have all moving parts protected by a guard.
The scope of supply shall include all the necessary compressed air system complete with compressors, coolers, necessary isolating and non return valves, pressure relief valve, water separators, silencers and vent pipe work, which shall be ducted to a safe discharge outlet.
For second stage conveying (i.e. for transportation of ash from surge/buffer hoppers to main storage silos)
(a) Three (3) nos. ash transportation lines (i.e. two (2) working + one (1) standby shall be provided for each unit.
(b) 3×50% capacity compressors shall be provided.
(c) The capacity of transport air compressors shall be decided to match the capacity of extraction system i.e. the capacity of extraction and transportation system shall be similar.
The output from each set of working compressors (as applicable), expressed as free air delivered (FAD) at ambient conditions, shall be as indicated in accompany data-sheet. At least 10% margin shall be provided on compressor capacity over and above the maximum flow requirement. 50 Degree C ambient and a RH of 100% shall be considered for design of capacity of compressors.
Compressors shall be screw type. All air compressors and their drives provided under this contract for a particular duty.
The compressed air in contact with the fly ash shall not contain oil exceeding 5 ppm. Therefore, oil injected compressors should be provided with associated oil separators to ensure oil not exceeding 5 ppm in compressed air system. Another essential requirement is for ‘dryness’ of the compressed air, and to achieve it, bidders shall offer a compressed air system which includes a moisture removal system. This system should comprise of a refrigeration type dryer.
Each compressor shall have an inlet filter of dry type to protect the compressor. The filter inlet area should be large enough to ensure frequent filter changes are not required.
A crank shaft driven positive displacement lubricating pump shall be used for lubricating the bearings and any other parts needing lubrication.
Cooling water requirement, if any, shall be arranged by the bidder.
Bidder shall include an inlet and/or outlet silencer so that each compressor unit complies with the noise requirements.
2.8.16.1 Air Receivers
Each compressor shall be provided with an air receiver of ample size of so that delivered air pressure is kept within ± 5% of rated pressure without excessive start/stop operation in the working cycle.
Air receivers shall be located convenient to compressor discharge. The receivers and associated fittings shall comply with BS:5169 and BS:1123 or other approved standards.
The receivers shall be supplied complete with test certificate, safety relief valve, fusible plug, pressure gauge, flanged inlet and outlet connections, inspection manhole (in accordance with Clause 25.2.4 of BS:5169-1975, or similar international equivalent), screwed drain connection, automatic drain trap with balance line, drain trap isolating valve, balance.
Line isolating valve and manual drain valve, nameplate, support frame or legs, and a set of suitable foundation bolts.
As far as possible the design, manufacture and performance of air receivers shall be in accordance with the following latest applicable standards :
(1) IS:2825 – Code for unfired pressure vessels.
(2) ASME-Sec. VIII Div.-1 Code for unfired pressure vessels.
(3) BS:487 – Fusion welded steel air receivers.
(4) IS:7936 – Air receivers for compressed air installations.
2.8.16.2 Water Separators
The Bidder shall supply water separators complete with automatic drain traps. Each separator shall be rated for twice the individual compressor flow at 1 bar above maximum operation pressure. Each water separator shall have flanged connections.
2.8.16.3 Drive Motor
Drive motor shall be connected to the Air compressors directly or through any suitable type of power transmission system. In no case V-belt drive would be used.
The continuous motor rating (at 50°C ambient) shall be at least ten percent (10%) above the maximum load demand of the compressor in the entire operating range to take care of the system frequency variation. Total maximum load demand shall include air compression power plus any power consumed in auxiliaries like cooling fan etc. When the driver is not directly coupled to the compressor, due account shall be made for losses in power transmission in addition to the above 10% extra margin.
2.8.16.4 Instruments
Each compressor shall be provided with the following instruments as a minimum:
a) Outlet air pressure gauge : 1 No.
b) Outlet air Pressure switch : 1 No.
c) Outlet air temperature gauge : 1 No.
d) Temperature switch (to sense
compressor high temperature) : 1 No.
e) Differential pressure switch across
separator element : 1 No.
f) Differential pressure switch across
suction air filter : 1 No.
g) Differential pressure switch across oil filter : 1 No.
h) Temperature gauge at the inlet and
outlet of oil cooler : 1 No. each
j) Low level switch in the oil tank : 1 No.
k) Pressure gauge in the equipment cooling
water supply line : 1 No.
l) Pressure switch or Flow switch in the
equipment cooling water supply line : 1 No.
m) Remote (control room panel mounted) pressure indicator along with a pressure transmitter at the outlet header of the compressors
n) Power On indicator light.
o) Service hours-run meter.
p) Load hours-run meter.
q) Motor overload (indicator light).
r) Fan motor overload (indicator light)
Operation of items ‘d’, ‘j’, ‘s’ and ‘t’ shall cause the compressor to trip.
The bidder shall include any other instrument required to make the system safe, efficient and reliable.
shivajichoudhury
