Keith Engineering (Australia) Pty Ltd ABN 20 109 344 185 20 Kellet Close, Erskine Park, NSW 2759 PO Box 354, St Clair NSW 2759 T +61 2 9852 1000 F +61 2 9852 1001 admin@keitheng.com.au www.keitheng.com.au MINTRAC MEAT INDUSTRY ENVIRONMENT CONFERENCE WASTE HEAT RECOVERY FROM RENDERING PLANTS PRESENTED BY DEREK HENDERSON
2 Processing of animal by products is simply a method of Dewatering the Raw Materials and the separation of the end products Tallow & Meat Meal. This process is referred to as Rendering. Raw Material Tallow Meat Meal
3 The by product of rendering is heat energy lots of it!
4 Every kilogram of moisture evaporated in the drying, or cooking process represents 2,257 of heat energy. Every kilogram of moisture evaporated from the cooker consumes approximately 1.3kg of boiler steam. Every kilogram of steam produced by the boiler consumed approximately 2,600 of Gas Energy.
5 SO WHAT IS A KILOJOULE? A kilojoule is 1,000 Joules and a Joule is a unit of energy and energy is what we want to recover. There are 1,000 kilojoules () in a megajoule (MJ) - and a MJ of natural gas costs, depending on your consumption, approximately 1 cent/mj. Your own records will confirm your own specific actual gas cost per MJ. So, looking at 2,600 (2.6MJ) of gas required to generate a kg of steam from the boiler at a cost of 1 cent/mj gas, this equals 2.6 x 1 = 2.6 cents per kg of steam. From the previous slide we have advised that approximately 1.3kg of boiler steam is required to evaporate 1kg of moisture from the cooker, or dryer. Therefore; 2.6cents x 1.3 = 3.38 cents. This is the cost of gas alone to evaporate 1kg of moisture from the cooker or dryer.
6 REMEMBER every kilogram of water evaporated from the cooker, or dryer has an energy value of 2,257, or 2.257MJ which can be recovered and effectively subtracted from the total plant energy consumption, or gas cost. 2,257 recoverable per kg of cooker/dryer evaporation = 2.257MJ x 1 cent per kg = 2.257cents/kg In summary 3.38 cents is the gas cost to evaporate a kg of moisture, and we can theoretically recover 2.257 cents per kg of evaporation! This is over 65% Energy recovery!
For Example 7 If we consider a rendering operation processing 100 Tonnes per day of red meat raw material having a yield of 45%, ie, 55 Tonnes of water to evaporate per day. 55 Tonnes of water = 55,000kg 55,000kg x 2.257 cents of recovered gas value per kg evaporation = $ 1,241 per day Times 5 days per week = $ 6,205 per week Times 50 weeks per year = $ 310,250 pa This is a theoretical fact, so if you have a use for waste heat, use it, this is what it is worth to you, on a relatively small rendering plant.
8 If you saw this you would do something right? Well see it, this is what it looks like. DO SOMETHING!
9 WHAT? As Mintrac members, this tells me you have an abattoir associated with the rendering plant. An abattoir uses a lot of hot water and the production of this is the best possible use for a rendering plants waste heat energy. If the rendering plant was not associated with an abattoir, or meat works and there was no requirement for hot water, then this advice may differ. Do not consider that any so called, High Efficiency Rendering Plant, has any energy benefit to offer you until an energy balance, or energy study has been carried out - and if your abattoir needs hot water, then take this saving into consideration.
10 Water has a specific heat capacity of 4.187/kg/⁰C. What does this mean?
11 This means that every kilogram of water requires 4.187 of heat energy, for every degree centigrade that the water temperature is increased. For example; to raise the temperature of 1kg of water from 20⁰C to 85⁰C, ie, an increase of 65⁰C will require 4.187 x 65 = 272. Remember that we have 2,257 to recover from every kg of water evaporated from the raw material in the rendering process. Therefore 2,257 272 = 8.3 Litres. This means that for every kilogram of moisture evaporated from the raw material in the cooking, or drying process that you can theoretically heat 8.3 litres of cold mains water at 20⁰C to 85⁰C hot water for use in the abattoir. We generally suggest, by rule of thumb and for budgetary purposes, that a practical figure of 7 litres per kilogram of cooker/dryer evaporation be used. This lesser volume covers heat loss in the process, which is generally between 10 and 15%. Obviously the less the temperature difference actually required, the greater the amount of hot water that can be produced per kg of cooker/ dryer evaporation.
m= Q c. t 12 For those of you who wish to be more adventurous or exact, this is the basic equation required: Where Q represents the quantity of heat energy to transfer c the specific heat capacity of water, ie, 4.187/kg/⁰C as previously explained t the change in temperature the water is required to undergo m which we are calculating, represents the mass of water that will be produced. (1kg = 1 litre) This calculation can become much more complicated if we are to consider heat transfer coefficients, radiated heat losses and the like, however from experience and as previously mentioned this will amount to a reduction of around 10% to 15%.
13 WASTE HEAT RECOVERY Waste heat in the form of steam generated by the cooker or dryer can be exchanged to water in what we call a Waste Heat Recovery Plant, this consists of the following; A Vertical shell and tube vapour condenser B Hot water storage tank C Plate heat exchanger D Cooling Tower
A Condenser B Hot Water Tank C Plate Heat Exchanger D Cooling Tower 14 E
WASTE HEAT RECOVERY PLANT 15 WASTE HEAT RECOVERY How does PLANT this work? E
Cooking Vapours Vapours exhausted from the cooker, or dryer 16 are ducted to the condenser and pass through the inside of the tubes. Drain E
Cooking Vapours Potable cooling water at ambient temperature is circulated around the outside of the tubes. Heat is exchanged from the vapours passing through the inside of the tubes, to the cooling water. This exchange of heat condenses the vapours which gravitate to the drain and in exchange heats the cooling water, which exit at a controlled temperature. Drain E
A thermocouple located at the hot water discharge monitors the temperature of the exiting heated water. 18 Thermocouple E
Thermocouple The thermocouple via a smart controller modulates the inlet water control valve to maintain the required, pre-set hot water outlet temperature. As the outlet temperature increases, the valve automatically modulates open and allows more cold water to enter and vice versa, thus controlling the end point hot water temperature up to 90⁰C. 19 Control Valve E
At times when hot water is not being used at a sufficient rate and depending on the storage capacity available for hot water, there may come a period when the hot water tank is full. At this time the mains water supply is automatically closed and the circulation valve opened. Main Supply Valve Circulation Valve E
Simultaneously, the hot water circulation Pump is started. The cooling tower is started. The water removed from the hot water tank is pumped through the plate heat exchanger and returned to the condenser preventing the loss of any water to the drain. 21 Cooling Tower Plate Heat Exchanger Water Recirculation Pump E
At times when the hot water tank level again reduces the mains supply is automatically opened and the recirculation valve closed. Simultaneously, the hot water circulation pump is stopped along with the cooling tower. Cooling Tower 22 Water Recirculation Pump Main Supply Valve Circulation Valve E
With the system set up in such a fashion no water is lost to the drain and the system is fully automatic. 23 E
Cooking Vapours Hot Water Tank 24 Thermocouple QUESTIONS? Condenser Cooling Tower Plate Heat Exchanger Water Recirculation Pump Control Valve Drain Circulation Valve Main Supply Valve E
25 WHAT ELSE?
26 WASTE HEAT EVAPORATOR PLANT Waste heat in the form of steam generated by the cooker or dryer can be used to evaporate stick water from a blood process, or from a low temperature rendering plant where the concentrated slurry can be returned to the cooker or dryer, increasing yield and protein otherwise lost to the drain. This is carried out by what we call a Waste Heat Evaporator Plant. This consists of the following; A Slurry Evaporator B Stick Water Holding Tank C Vacuum Condenser D Cooling Tower
WASTE HEAT EVAPORATOR PLANT 27 A Slurry Evaporator How does this work? B Stickwater Holding Tank C Vacuum Condenser D Cooling Tower
vaporator E Vapours from Cooker or Dryer Vapours exhausted from the cooker, or dryer are ducted to the evaporator and pass around the outside side of the tubes. Drain 28
vaporator E Vapours from Cooker or Dryer The condensate formed passes through an airlock to the drain. Any steam not used in this process continues to the existing vapour condenser to produce hot water, as previously described. Drain 29
vaporator E Vapours from Cooker or Dryer The evaporator, or series of evaporators can be sized to utilise all of this waste heat, if required. Drain 30
Stick water is pumped at a controlled rate to the evaporator and passes through the inside of the tubes. This gravitates to the slurry tank from where it is recirculated back to the top of the evaporator to pass again. Stickwater Tank Slurry Tank Concentrate to Cooker 31
Recirculation continues until the desired concentration is achieved when the concentrate is metered out of the system and fed to the cooker or dryer. Stickwater Tank Slurry Tank Concentrate to Cooker 32
The metered in raw stick water and metered out concentrate are balanced and controlled via a smart controller. Stickwater Tank Slurry Tank Concentrate to Cooker 33
A vacuum pump creates a negative pressure within the tubes of the vacuum condenser - the ducting to the slurry tank - within the slurry tank and through the tubes of the evaporator. Vacuum Pump -kpa 34
This vacuum allows the stick water to boil at a lower temperature using the heat exchanged from the 100⁰C steam passing around the outside of the evaporator tubes. Vacuum Pump -kpa 35
The vapours driven off the stick water in this process are condensed in the vacuum condenser as in the Waste Heat Recovery Plant previously described. Vacuum Condenser Cooling Tower Drain 36
This exchanged heat is rejected by a cooling tower and returned to the vacuum condenser for reuse as cooling water. Vacuum Condenser Cooling Tower Drain 37
Again, hot water can be recovered from the vacuum condenser as previously explained with the Waste Heat Recovery Plant. 38
Slurry Evaporator Vapours from Cooker or Dryer QUESTIONS? Stickwater Holding Tank Slurry Tank Cooling Tower Vacuum Pump Vacuum Condenser Drain Concentrate to Cooker Drain 39
FLASH STEAM RECOVERY 40
FLASH STEAM RECOVERY Any steam heated vessel, such as a cooker, or dryer which return their spent steam as condensate back to the boiler for reuse, generate flash steam. 41 Flash steam occurs when pressure is relieved from the pressurised condensate. For example, at 100⁰C at atmospheric pressure (0kPa Gauge) water is converted to steam. A steam trap releases condensate (water) from the cooker to the condensate return pipe at say 200kPa Gauge, which relates to a temperature of approximately 133⁰C. When 133⁰C water is released to atmospheric pressure in the boiler feed water tank it immediately converts to steam. This heat energy and treated return water is as such lost to the atmosphere.
42 This waste heat energy again can be harnessed and effectively utilised. Craig McKnight from Spirax Sarco is going to be talking to you tomorrow about flash steam and condensate heat in his segment - and how this can best be used to enhance boiler performance. I encourage you to attend this, as it is a great system they offer.
43 SOMETHING TO THINK ABOUT Think outside the square. As humans our thought patterns are pre-programmed and instinctive. Other methods of heat recovery and uses for waste heat exist and the answer is not yet apparent to us. Just as car manufactures have a major issue in how waste heat from their engines can be put to better use to improve efficiency so do we renderers. There are more cars on the planet than rendering plants and more car manufacturers than rendering equipment manufactures and they do not yet have the answers.
AND YOU THINK WE HAVE WASTE HEAT ISSUES! 44
45 SOMETHING TO THINK ABOUT Again, I believe we are conditioned to a thinking pattern and the answer is out of that conventional thinking. We need to be less mainstream in our thinking if we want to find more answers. With this in mind - my message to you all is simple.
46 DO SOMETHING! EVEN IF YOU JUST THINK ABOUT IT!