Pumps

date2025-05-11tags:meche:

System Curves Tutorial

A system curve shows total head loss across flow rates. Head loss has two parts: static head and dynamic head. Dynamic head includes frictional losses (major) and component losses (minor). Static Head

Static head includes elevation and pressure differences between supply and destination. It remains constant regardless of velocity. Calculate it with this equation:

(1.A.1) Î”hstat=(zdestinationâˆ’zsupply)+(Pdestinationâˆ’Psupply)Ïg

where:

z is elevation, in feet P is pressure, in psi Ï is fluid density, in lbm / ft3 g is gravitational acceleration, 32.2 ft/s2

Note that if the supply and destination are at the same pressure, as is the case when they are open tanks, then the static head is simply the difference in the liquid elevation. Frictional Head (Major Losses)

Head loss from friction depends on flow rate (velocity). Calculate it for each system component: piping, valves, elbows, bends, and end-use equipment. These losses scale with the square of velocity.

Frictional head losses in pipes can be calculated using the Darcy-Weisbach equation. The Darcy-Weisbach friction factor, f, can be determined using the Colebrook-White equation (defined in Fluid Flow â€“ General).

These equations will approximate the Moody diagram. The friction factor is based on the Reynolds Number (Re), the pipe diameter (Dh), and the pipe roughness (Îµ). The pipe roughness is dependent on the type of pipe being used. Other aspects, such as age, fouling, and coatings will also affect the pipe roughness.

The Hazen-Williams equation is another method to determine pipe losses. These values are only valid for water and do not account for temperature or viscosity. These values are a function of pipe material only and are not dependent on Reynolds Number. A table of typical values for various pipe materials can be found here. Minor Losses

Minor losses in a piping system occur when fluid passes through a fitting, valve, area change, or enters or exits a tank, etc. Any system component that obstructs or changes the direction or pressure of the flow can be considered a minor loss. These are categorized differently than the pipe frictional loss (or major loss). These minor losses can be the dominant system loss.

The loss created by the component is often characterized by a constant, K, and tabulated for several types of components. Head loss is determined by the equation defined in Fluid Flow â€“ General (K values are also tabulated here).

Notes to Dr Rui

Dear Dr Rui,

Please find below some notes from our meeting. I am looking at Dubai-based vendors as an initial start, will keep you updated on replies and concerns from vendors. Please share the PID diagram with me, if you don't mind.

Was lovely meeting you again! Looking forward to our next meeting.

Regards, Vishakh

Context: Electrolyzer pressure is to be increased for better efficiency and wider industry application. Along with higher pressure and capacities comes the need for new parts that can handle the new operating environment (which is still corrosive KOH at high temperatures). Thankfully, the oil and gas sector has had similar requirements for a while, so they should be a starting point for procuring parts. Location of vendor is not an issue for now, need an indication on pricing more importantly.

Items that need to be procured: Drain valve (ball check valve) Meant to periodically drain water back to the tank. Needs to be 316l SS to be compatible with existing equipment. Should be able to handle 15-16 bar for the medium pressure 10 bar scenario, as well as 35(?) bar for the 30 bar scenario.

Designer/Fabricator for pressure vessels Pressure vessel is for gas separator, needs to be 316L SS, for a design pressure of 35 bar.

Pumps & VFD Pump suction and discharge should be rated for 35 bar. Flange connections are to be 300% pressure rated in order to handle operating pressure and temperature. Given the corrosive electrolyte (1-2M KOH at 70C), material selection is important. Motor needs to handle a flow rate of 7 m3/hr at head of 21m (likely a 1.2 kW pump). Given that the pump is running 24/7, power efficiency for BOP is a priority. VFDs for small pumps tend to be expensive, so a combination of the two will be helpful. Single-phase VFD should suffice (and can be run from 3-phase system).

Deoxo (Oxygen Depletion system) and TSA (themal swing adsorption gas dryer) Used to achieve high gas purity, although with loss of hydrogen (15%!) so high efficiency is needed.

Sensors

Flowmeters, Temperature sensors, and pressure sensors (generic process control, PAH, TAH, FAH. Might need to consider LAH and HH/LL alarms as well?)
Electrical conductivity probes (electrolyte monitoring)
Dew point temperature sensors (for drying)
O2 in H2, and H2 in O2 sensors (for safety)

Note: Not a High priority, given existing sensors, but needed for 10bar and 35 bar.