What is Delta T?

Delta T is an innovative method of controlling the MC of solid products being dried. It is not based upon IR, RF, capacitance, etc., or any of the traditional methods of moisture measurement.  Delta T is different and it's better!

The basis of the Delta T moisture sensor is two temperature measurements: Thot (hot side) and Tcold (cold side) and a math model derived from first principles.  The hot side temperature is defined as the temperature of the hot air immediately before contacting the product; and the cold side temperature is defined as the temperature of the air immediately after contacting the product.

The difference in these two temperatures, ΔT (delta t), is related to the product moisture content by a mathematical model derived from first-principles.  Drying Technology, Inc. patented this method of moisture sensing and control utilizing the delta t process variable that is applicable for batch and continuous drying using direct and indirect drying.

 

How is the Delta T different?

Delta T is the only system that can sense moisture inside-the-dryer! Our patented, model-based approach has found acceptance where conventional sensors cannot be located inside the dryer (i.e. high temperature, wet, dusty environments). Temperature probes can be located essentially anywhere in the dryer and that's all that is needed for the Delta T method.

By sensing moisture inside-the-dryer, the dead-time (time required to detect a water load change entering with the feed) is significantly reduced. Consequently, disturbances entering with the feed are corrected before the product exits the dryer resulting in a minimum 30% reduction in the product moisture variation exiting the dryer.

 

What makes the Delta T better?

• Based on an "inside-the-dryer" sensor
• Based on a first-principals model
• Requires no calibration
• Operator friendly
• Reduces MC variation by 30%

Dryers do a fairly good job of maintaining consistent temperatures and airflow throughout the dryer, but they lack a mechanism to automatically adjust to variations entering the dryer (i.e. wetter/drier product or changing production rates). The Delta T is superior because it automatically makes the necessary adjustments to the drying conditions (i.e. heat input or belt speed), as needed, to correct for the variations before the product exits the dryer. Again,this will reduce the moisture variation in the product.

 

How was this method developed?

The patented Delta T model for dryer control was mathematically derived from first principals:

MC = K1(ΔT)p-K2/Sq

where MC = exit product moisture; ΔT = temperature drop of hot air after contact with the wet product; S = production rate or dryer speed; K1, K2 = constants unique to a system and product; p,q = exponents unique to a system and product.

For batch dryers, dryer speed is converted to drying time (Dt) and the model becomes:

MC = K1(ΔT)p-K3(Dt)r

 

What are the benefits of a Delta T?

The Delta T Dryer/Moisture Control System will reduce the product moisture content variation. This reduction directly results in:

• Production Increases - average moisture content can be raised to sell more water
• Energy Savings - eliminates over-drying
• Product Quality Improvements - consistent, on target moisture content
• Rapid Payback or Return-on-Investment (ROI)

What are some of the features of the Delta T?

The following is a partial list of features of the Delta T Dryer/Moisture Control System:

• Automatic and continuous control
• Automatically adjusts to production rate variations
• Integration into existing control hardware
• No calibration required
• Cruise control startup
• Based on a rugged, reliable moisture sensor

What does a system consist of?

A Delta T Dryer/Moisture Control System consists of:

• Delta T software
• PC if not available on site
• Input/output devices (i.e. PLC) if not available on site
• Temperature probes (RTD's or thermocouples)

Drying Technology, Inc. always supplies Delta T software and will supply a PC and I/O if necessary.  Some customers already have I/O devices (PLC, Opto -22) and HMI's (Human-Machine-Interface), e.g., like Wonderware, in place.  In this case we would supply software only.  In short, we supply software and any level of hardware that is needed.  We do not sell hardware per se, we sell technology and will utilize your existing control hardware.

Temperature probes are supplied and installed, as well as all wiring/conduit, by the customer. At most plants, temperature probes are held in reserve for maintenance purposes and it is usually easier for customers to supply and install them. We can, however, recommend vendors with specific temperature probe part numbers if needed.