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Contenuto archiviato il 2022-12-27

ENERGY SAVING IN DRYING PROCESSES

Obiettivo

OBJECTIVES :
1) To incorporate moisture extraction measurement rakes in a range of representative types of hospital laundry batch tumble dryers.
2) To carry out a detailed monitoring exercise on each dryer in order to establish the effectiveness of the moisture extraction measurement system as a control system in achieving energy saving.
3) Following the monitoring study, to assess and report on the cost effectiveness and reliability of the system.
4) To adopt a target technical/economic objective of energy savings around 25%, as compared to energy use when drying under to control of "conventional" systems.
In the project, system changes by the laundry operators and problems encountered with the relative humidity sensor, the key component of the moisture extraction measurement instrumentation resulted in a re-definition of the project aims.
The modified aims allowed further development of the relative humidity sensor and associated system, but with a reduced demonstration phase.
A series of datum test runs were undertaken on the PASSAT type dryer during June and July 1988. In all cases steam flow and airflow were recorded. Based on past test experience, the measured values agreed well with the manufacturer's values, given that dryer actual steam consumption and airflow vary with site conditions, dryer installation and type of washload. From the tests it was found that steam usage is governed by the air heating load on the battery. This allows energy use to be directly linked to dryer 'on' time. Thus a reduction in drying time results in a saving in energy use on a directly proportional basis. Following the project hold, the full test programme on the Passat and ORTEX dryers covered a range of wash loads and drying times. Two candidate RH sensors were used.
The key findings from the combined series of tests over the two stages of the project are as follows :
(i) Average values of relative humidity and temperature have been successfully measured in the exhaust ducts of operating large batch tumble dryers.
(ii) The measurements have been carried out on a dynamic basis allowing sufficient time resolution for effective dryer control.
(iii) For full drying cycles, the proposed basis of control is a combination of the RATE of change of RH and specific humidity with time. This has been confirmed to be effective.
Through application of the new control/calibration device to the FULLY FIELD wash cycles at Groby Road laundry, drying energy savings of 20% were achieved.
The contract for the projct was originally let by CEC Directorate 17 to the Leicestershire Health Authority (LHA) at directorate level, now embodied as the Estates and Fcailities Dept. Glenfield NHS Trust. All technical aspects relating to installation, instrumentation, site test and data analysis were subcontracted to GEC-Alsthom, ERC (Whetstone), now embodied as, MEC, European Gas Turbines Ltd.
The project was based at the Groby Road Hospital central laundry of the LHA. The hospital authorities made available two examples of large batch tumble dryers for the project test series; these were the PASSAT 253.15D and the ORTEX 74151.
To meet the project objective of control of the drying process on the basis of the dryer exhaust moisture condition, the key parameters monitored were the exhaust flow relative humidity (RH) and temperature. This was achieved using an (area weighted) averaging rake sited across the exhaust duct to take a representative flow sample. A measuring volume, closed-coupled to the rake, incorporates sensors allowing RH and temperature levels to be established. Temperature measurement is by a platinum resitance thermometer, type 4-wire, class B and RH measurement by a fast response, thin film polymer based, capacitive sensor.
The basis of the control philosophy is that drying is terminated when the moisture extraction rate reaches a predetermined level (see results section). Energy saving is achieved through minimising the drying time. The level of saving is assessed by comparison with previous drying practice. Work commenced in October 1987. Subsequent to sourcing of instrumentation, components and device manufacture, an installation and commissioning phase took place from March to May 1988.
Preliminary tests and datum test runs took place in June to July 1988. Following the problems noted in the previous section, the project was re-started in mid-1992. After necessay re-commissioning, a development test series was run on the PASSAT andORTEX dryers from October 1992 to March 1993.

Argomento(i)

Invito a presentare proposte

Data not available

Meccanismo di finanziamento

DEM - Demonstration contracts

Coordinatore

LEICESTERSHIRE HEALTH AUTHORITY
Contributo UE
Nessun dato
Indirizzo
GLENFIELD NHS TRUST GLENFIELD HOSPITAL, GROBY ROAD
LE3 9QP LEICESTER
Regno Unito

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Costo totale
Nessun dato