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York Steam Fired Backpressure Problem

York Steam Fired Backpressure Problem

(OP)
@YPC-ST-400 G-model, max 7bar steam
running parameters 3.4-3.8bar steam, ~2bar cooling water @30Celsius in 35celsius out, LiBr S.G at absorber outlet (solution pump discharge) ~1.62



Green Arrow: Temp sensor dilute solution to HTG from HXchanger
Red Arrow: Temp sensor Concentrated solution leaving HTG to HXchanger
Brown Arrow: Pressure sensor HTG vapours to LTG tube side
Blue Arrow: HXchanger condensate heat recovery

Drain cooler (blue) was replaced beacuse too many of its tubes (twisted Cu, carrying LiBr) developed leak, new HX was installed to replace original, however, the new HX didn't have twisted but plain tubes ..therefore expect lesser heat transfer coefficient than original. This replacement I include may or may not relate with the current problem I face!

Whenever the startup if this chiller is required (boiler/pipelines maintenance) we have to face a delay time stretching more than ~6hrs. Assume a proper chiller shutdown after 1-2 dlution cycles.

When the steam pressure is increased at startup we witness that solution temperature (Green) isn't rising, with increasing steam its temperature increment is too slow plus the HTG pressure (Brown) isn't rising too, however, HTG solution temperature (Red) is rising at a rate much faster ...thus machine trips when it reaches ~121celsius. There is another observation ...instead of condensates at the outlet of drain cooler now it's wet steam, making our chiller appear like a jet rather than a refrigerating machine :whistle: Increasing seam pressure at this moment further increases HTG temperature (increasing temperature trip probability) as well as jet noise without increasing either HTG pressure or Solution temperature, thereby machine remains at ~19celsius outlet chilled water temperature instead of ~12celsius.

Refrigerant quantity in this model is the sum of two elements: First condensates (shell side, via condenser) of vapours generated in LTG, second condensates (tube side, after heat transfer to LTG solution) of vapour generated in HTG. Vapours generated in HTG (Brown) if low are bound to decrease refrigerant quantity generated overall ..because now heat medium provided to LTG is low (2nd element) which in turn decreases vapours generated by LTG (1st element)

To curb the problem I reduced the cooling water pressure from ~2bar to ~1.5bar, in an attempt to increase both HTG pressure (by decreasing rate of condensation in condenser) & solution temperature (reduced cooling water flow to absorber). Steam pressure was then fine tuned by manual adjustements by a diaphragm valve upstream of control valve. Whenever steam was increased by an increment of say ~0.4bar, roughly a backpressure of ~1bar was registered by pressure gauge downstream of control valve, machine was then operated at this position for ~45mins which decreased the backpressure by half, also lessened jet noise indicated more condensate rather than wet steam at drain cooler outlet. Steam was incremented in a similar manner until solution temperature rises (without too much rise in HTG solution temperature) ..but this length process was highly repetitive & boring

Now my question is why the jet & why not the condensates. Why solution temperature & HTG pressure not rise with a rate as experienced before when machine was normal. Increasing cooling water pressure makes HTG pressure to decrease & jet problem resurfaces ...with pressure gauge reading in excess of ~6.5bar.

The problem is not solved as decreasing Cooling water pressure has badly affected absorber preformance & now chiller maintains ~15celsius chilled outlet

RE: York Steam Fired Backpressure Problem

Obviously changing to plain tubes has affected the performance of this absorption unit. I would contact the manufacturer and determine if twisted inserts could be fitted inside the tubes to increase the heat transfer. You'll see such inserts inside plain tubes of fired domestic hot water storage tanks.

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