GB2032775A

GB2032775A - Combustion prevention systems for spray drying equipment

Info

Publication number: GB2032775A
Application number: GB7842806A
Authority: GB
Original assignee: Aberdeen & District Milk
Current assignee: Aberdeen & District Milk
Priority date: 1978-11-01
Filing date: 1978-11-01
Publication date: 1980-05-14
Also published as: NL7907995A; DE2944384A1; DE2944384B2; FR2440532A1; BE879753A; DK460979A; AU5238279A; SE7908946L; DE2944384C3; FI793387A; YU264479A

Abstract

The invention relates to combustion prevention systems in spray drying equipment of the type in which a concentrate of wet products is fed by a product pump to an atomiser in a drying chamber where hot swirling air dries the product, the equipment normally being provided with automatic fire extinguishing equipment. The combustion prevention system comprises a first change-over valve 16 located downstream of the product pump 4 to introduce water to the product line 3 when a pressure switch 19 in the product line upstream of the product pump senses a pressure drop in the line caused by reduced product output or no product output from the pump. A second change-over valve 20 located in the product line upstream of the pressure switch 19 provides for introducing water delivered by a pump 23 to the product line when the product pump fails and causes an over-temperature in the drying chamber, the over-temperature being sensed by a temperature sensing device which actuates the second change-over valve 20 at an over-temperature less than the over-temperature necessary to actuate the fire extinguishing equipment. <IMAGE>

Description

SPECIFICATION Combustion prevention systems for spray drying equipment This invention relates to combustion prevention systems for spray drying equipment.

Spray driers which are used for drying products by atomising moist products in a drying chamber supplied with hot air are subject to fire or explosion conditions if critical temperatures are exceeded.

Normally the products to be dried in a spray drier are in the form of a concentrated liquid or slurry which is held in a hopper or holding tank and fed from the tank through filters to a pump which delivers the concentrate to an atomiser in a drying chamber. The atomiser sprays the concentrate into a mass of swirling hot filtered air normally in the region of 180"C. The hot air is normally delivered to the drying chamber adjacent the atomiser at the top end of the chamber and instant drying of the concentrate takes place. The dried concentrate is in the form of a powder which falls to the base of the drying chamber where it can be extracted or further processed. An outlet adjacent the base of the drying chamber may be provided for drawing off very fine powder, resulting from the drying process, which is recycled.

Such spray driers are subject to fire or explosion conditions caused by over-temperatures in the drying chambers and automatic fire extinguishing equipment is normally fitted to such spray driers.

Such fire extinguishing equipment normally consists of a water storage tank connected through a pump to spray pipes located around the periphery of the drying chamber to flood the spray drier in the event of critical fire/explosion conditions. Critical overtemperatures in the drying chamber are sensed by a temperature sensing device which actuates the fire extinguishing equipment.

Such spray driers as above defined are hereinafter referred to as spray drying equipment.

The main causes of over-temperatures which lead to firefexplosion conditions in such spray drying equipment is the loss of product to the product delivery pump or failure of the pump which results in loss of product at the drying chamber.

Normally a fire/explosion condition is merely reached before the fire extinguishing equipment becomes operative and the spray drying equipment is flooded by the fire extinguishing equipment to prevent fire. Mopping up and drying the spray drying equipment is therefore necessary after actuation of the fire extinguishing equipment resulting in loss of production for some time.

There is a need for the spray drying equipment to be kept as near to normal working temperature as possible so as to avoid fire/explosion conditions being reached when the automatic fire extinguishing equipment would be actuated.

The present invention provides a system whereby the spray drying equipment is kept as near as possible to normal working temperatures when there is product failure to the drying chamberthus avoiding fire/explosion conditions being reached which would actuate the automatic fire extinguishing equipment.

According to the invention combustion prevention systems for spray drying equipment of the type defined includes a pressure switch interposed in a product line of said spray drying equipment on the upstream side of the product delivery pump to sense a pressure drop in said product line and to a signal a first change-over valve located in the product line downstream of the product delivery pump to change the supply to said pump from product to water supplied from the water source, a second change-over valve located in said product line upstream of the pressure switch to change the supply to the atomiser from product to water and vice versa, said latter water being supplied from a source through a water pump to the atomiser, and a temperature sensing device to sense the temperature in the drying chamber of said spray drying equipment, said second change-over valve being actuated by the temperature sensing device to change from product supply to water supply at a predetermined overtemperature and to change back to product supply at a predetermined working temperature.

A preferred embodiment of the invention is illustrated by way of example in the accompanying drawing which illustrates a schematic layout of spray drying equipment of the type referred to with a combustion prevention system according to the invention.

Referring to the drawings spray drying equipment comprises a drying chamber denoted at 1 having an atomiser 2 located adjacent the top of the chamber 1 and connected by a pipe line 3 through a product delivery pump 4 from a holding tank 5 which contains a product to be dried. The product to be dried normally being in the form of a concentrated liquid or slurry which is prepared and supplied to the holding tank 5.

The product is delivered by the pump 4 to the atomiser 2 where it is atomised and sprayed into a mass of swirling hot filtered air, normally at a temperature in the region of 180"C.

The hot air is supplied to the drying chamber 1 through a duct 6 adjacent the top of the chamber 1.

The dried product falls to the bottom of the chamber 1 from where it can be extracted or further processed.

The delivery line 3 is provided with a pressure relief valve 7, upstream of the product delivery pump 4 to relieve the line to the holding tank 5 when the pressure exceeds a predetermined value.

The spray drying equipment is provided wirh automatic fire extinguishing equipment which does not form part of this invention. The fire extinguishing equipment as illustrated comprises a water storage tank 10 connected through a pump 11 and solenoid valve 12 to spray pipes 13 located around the periphery of the drying chamber 1. A thermostat 14 senses the temperature of the drying chamber and actuates the solenoid 12 and pump 11 when critical over-temperatures are reached in the drying chamber.

Combustion prevention systems are provided which comprises an electro/pneumatic change-over valve 16 interposed in the product line 3 downstream of the product pump 4 and connected to a water circuit 17 from atank 18 and arranged to open the water circuit 17 into the product pump 4.

The change-over valve 16 is actuated by a pressure switch 19 interposed in the product line 3 upstream of the product pump 4.

The pressure switch 19 senses a pressure drop in the product line 3 when the line is starved of product and actuates the change-over valve 16 to provide water to the pump 4 which delivers the water to the atomiser in sufficient quantity to keep the drying chamber at approximately its working temperature until the malfunction in the product line is remedied.

For the event that the product pump 4 should fail and thereby starve the drying chamber of product causing an over-temperature a second electro/pneumatic change-over valve 20 is located in the product line 3 upstream of the pressure switch 19 to open a water circuit 21 into the product line 3 through a non-return valve 22 from a pump 23 supplied from a water source, which may be the tank 10 as shown.

The change-over valve 20 is actuated by a temperature sensing device, which may be the thermostat 14, or other suitable temperature sensing to sense the temperature in the drying chamber.

The temperature sensing device is set to actuate the change-over valve 20 to open the water circuit 21 and actuate the pump 23 when the temperature of the drying chamber exceeds its working temperature and to close the water circuit and stop the pump when the temperature of the chamber returnsto its normal working temperature.

Ideally the temperature sensing device should actuate the change-over valve at an overtemperature in the range 10-15 Coverthe normal working temperature i.e. before the temperature reaches its critical over-temperature to actuate the fire fighting equipment.

The water in the water circuit is supplied at a pressure slightly above the normal product pressure.

When the temperature returns to normal the water circuit 21 is closed and the pump stops but if no product reaches the drying chamber and the temperature again rises the change-over valve 20 is again actuated. The cycle, with its cooling effect within the chamber, has a repetitive action to give the necessary time to remedy any malfunction and return productions to normal with minimum disruption and thus avoid the operation of the main fire fighting equipment until fire/explosion conditions are imminent.

Claims

1. Combustion prevention systems for spray drying equipment ofthe type defined including a pressure switch interposed in a product line of said spray drying equipment on the upstream side of the product delivery pump to sense a pressure drop in said product line and to signal a first change-over valve located in the product line downstream of the product delivery pump to change the supply to said pump from product to water supplied from water source, a second change-over valve located in said product line upstream of the pressure switch to change the supply to the atomiser from productto water and vice versa, said latter water being supplied from a source through a water pump to the atomiser, and a temperature sensing device to sense the temperature in the drying chamber of said spray drying equipment, said second change-over valve being actuated by the temperature sensing device to change from product supply to water supply at a predetermined over-temperature and to change back to product supply at a predetermined working temperature.

2. Combustion sensing systems as claimed in claim 1 in which the first and second change over valves are electro-pneumatic actuated valves.

3. Combustion prevention systems as claimed in claim 1 or 2 in which the temperature sensing device is operative to actuate the second change-over valve when the over-temperature in the drying chamber is within the range 10-20"C above normal working temperature.