Tumble Dryer Exhaust Problem

[wilcox]

Hi all,

I have six tumble dryers and their exhaust are ducted and discharged to ambient. During their simultaneous operation, the exhaust air flow was found to be 2cub.m/s at 70degC. This hot odorous exhaust cause nusiance to my neighbours.

I am trying to use zeolite for odour removal yet its removal eff. would deteriate under high temperature and humid conditions(i.e. room temp. is more favorable). Would any prof. advise a effective way to cool down the exhaust air to room temp. for onward treatment. (My est. cooling load required would be about 120kW, pls correct me if I am wrong)

Thank you

 

[fredb]

Hello,

You might consider Heat-pipe type air to air heat exchanger. They are particularly efficient, and are available in many types of metals.

 

[ChasBean1]

What dewpoint (or humidity) at 70°C? For cooling load you should use Q = m dh: the mass flow of the air times the difference in enthalpies, 70°C, ??°C dewpoint, to design discharge value.

You'd also need another filter inline to protect the exhaust coil. The added resistance of a filter and a coil PLUS your zeolite medium in the exhaust stream could combine to make drying difficult (due to backpressure) if all run at once.

Could you gang all into a common exhaust duct that leads to a fan on the roof that discharges upward? What is the config. of buildings where people are complaining?

 

[mdonner]

I use an household dryer with embedded air-air HX.
The heated (secondary) air has no odor and has very low humidity. The primary humid hot air is cooled by the ambient secondary air, and the condensate water (from the primary hot humid air) is piped to the drain.
The additional required power is for the blower driving the ambient air through the HX.
You will need the value or the primary air relative humidity or due point temp for sizing the HX and secondary blower.

 

[wilcox]

Thank you so much for all your precious advices.

I have tried to source some sorts of heat pipe for that purpose. Yet the required cooling capacity would be considerably high (sensible cooling about 120kW)and the operation control of heat pipe would be complex. Is it a wise choice (in terms of capital and operation cost) in using heat pump system for co-generation of exhaust air cooling and hot water for the laundry? Any experience sharing?

ChasBean1: Your suggestion is pretty sound yet my laundry is on the ground floor of a 40-storey residential building. A lengthy central exhaust stack with booster fan would be required to duct the hot odourous air to high level. Residents of my building might kill me if I install the stack either interior area or along the building facade.

 

[Cooky]

You could install a water-to-water heat pump unit, using the cooling side to chill the hot exhaust air prior to entering the 'zeolite air cleaner'.

You could use the heating side of the heat pump to heat your domestic hot water supply (or at least part of it). If you have a constant demand for hot water there is no problem, but if it's intermittent, you may need a secondary source to reject the heat into. A secondary re-heat coil, fitted after the 'zeolite' unit could do this.

A good water-to-water heat pump will achieve hot water temperatures of 63 deg.C

 

[lilliput1]

Try mixing the exhaust with enough air to dilute the odor. Use an exhaust fan to draw in the dryer exhaust + OA for dilution & exhaust them as far as possible from air intakes/windows.