Reprinted from Drying Technology, 18(4&5), pp. 1147-1156 (2000)

Department of Chemical Engineering, McGill University

3610 University Street, Montreal, Quebec, Canada H3A 2B2

Keywords and phrases: Innovation; dryer types; statistics; patent abstracts; US patents

A preliminary semi-quantitative analysis is made of the recent patent literature related to drying and dryers. United States patents granted in the period January 1998 to June 1999 were examined. For this preliminary study, only the abstracts were used to classify the patents by subject area and arrive at some general conclusions. An in-depth overview covering a larger database and full texts of the patents is required to confirm the results presented.

The patent literature provides a useful indication of the scope and intensity of industrial interest in a given subject area. The magnitude of academic research activity as evidenced by the number of archival publications is not necessarily indicative of the level of industrial interest or activity in the field. Figure 1 shows the number of patent titles issued in the USA during 1990-1999 that include the words drying or dryers (driers). On average, nearly 240 such patents were issued in the USA per year; the number is much smaller for Europe (under 100). Figure 2 shows how the patents are distributed in several key industrial areas, e.g., freeze drying, spray drying, paper drying, sludge drying and grain drying. Although the academic research activity in drying is at a low level in North America and Western Europe, the patent activity is rather significant when compared to that in such other unit operations as evaporation, adsorption, crystallization, membrane separation, etc. (see Figure 3). It appears that there is little, if any, correlation between the number of patents granted in the United States and the academic research activity as far as the unit operations are concerned. It appears that academic research is not driven (or even guided) by current industrial needs or interests. Note that Figures 1 through 3 are based on searches of only the patent titles using the keywords drying and dryers (driers). Tables 1and 2 give the numbers of patents shown in Figures 2 and 3.

Figure 1. Number of US patents issued in drying/dryers

Figure 2. Number distribution of US patents in key industrial drying areas

Figure 3. Number of US patents issued in various unit operations

Table 1 shows one surprising statistic; drying of sludges and freeze drying did not reflect the increased interest in environmental pollution control and advanced materials/biotechnology, respectively. Not unexpectedly, grain drying also showed little patent activity with only 0-5 patents per year over the last decade.

Table 1. Number of US patents issued during January 1998-June 1999 which contain the words drying, dryer, drier and dried in title

* January 1998-June 1999

Table 2 clearly demonstrates the significantly larger number of patents issued in drying/dryers when compared with other key physical unit operations of adsorption, crystallization, distillation, membrane separations and evaporation. Although these areas do demonstrate increase in the numbers of patents issued, drying/dryers attracted more patent activity than all these operations combined. Surprisingly, membrane separations and crystallization show activity well below one would have expected in view of the rising academic interest in these areas.

Table 2. Number of US patents granted in key chemical engineering unit operations

* January 1998-June 1999

This note presents a semi-quantitative analysis of United States patents issued during the period January 1998-June 1999, which pertain to drying or dryers. It should be noted that analysis of a larger database covering longer periods as well as other databases (e.g., European, Japanese, Canadian patents) may modify the general observations somewhat. It is extremely difficult, if not impossible, to avoid duplication when merging patent databases of various countries. It is justifiably assumed that most commercially viable patents from all parts of the world are also filed with the United States Patent Office.

It is useful to note the level of patent activity in general in various countries. For example, between 1977 and 1994 the number of patents granted in Canada have declined from 22,800 to 11,600 while in the USA and Japan these numbers increased from 65,300 and 52,600 to 102,000 and 82,400, respectively. It is interesting to note that the number of patents in force in Canada, USA and Japan in 1994 were 321,000, 1,130,000 and 652,400, respectively. The corresponding figures for 1977 were 411,800, 1,096,000 and 351,000, respectively – a major decline for Canada and a major increase for Japan. Interestingly, the percent of GNP spent on R&D in Canada and Japan rose in this period while that for USA remained nearly unchanged at a relatively high value of 2.8.

Over 450 patents were retrieved from the U.S. database which contained drying or dryer (driers) in their title. Drying appears to be an area of appreciable concern to industry. The objective of this study was to identify areas of drying technology that have attracted significant level of industrial interest.

An attempt was made to classify the patents in one of the following categories:

• Drying equipment, operation (~15 percent)
• Drying of specific products (~60 percent)
• Other, e.g., mode of heat input, product collection, control, etc. (~25 percent)

As expected, a large fraction of the patent subjects could not be categorized clearly as above; many could be classified into two categories on the basis of the abstracts. No attempt was made to access the full texts of the patents for lack of relevant resources. In general, the patent abstracts are not clearly written; in some instances, it was impossible even to figure out what the objective of the patent was. Several patents issued to same claimants seemed remarkably similar in the content of the abstracts; it is likely that the set of claims made differ.

Innovation is understandably regarded as a hallmark of patented products or processes. On the basis of the abstracts alone, in a majority of cases, the element of novelty or innovation appeared to be missing altogether. Many patents cover ideas that should follow logically from a fundamental knowledge of the subject of drying and product characteristics – at least for those well-versed in drying technology. Indeed, a cursory perusal of the articles published in Drying Technology – An International Journal and proceedings of IDS would yield more creative and innovative ideas than one obtains by perusal of the patent abstracts; this could be a result of the "legalese" often used in describing patented inventions. Further, over 99 percent of the patents result from industrial or business rather than academic sources despite recent attempts by universities to actively pursue industry-driven R&D. Publicly available technical literature is full of ideas that are patented subsequently with minor tuning. There is a clear need for university-industry cooperation in developing new drying technologies.

Among the dryer-oriented patents, several patents issued during 1998-99 pertained to:

• Drying of paper or webs
• Drying of printed sheets; inkjet images, etc.
• Heat Pump Dryers
• Freeze and Spray Dryers
• RF and Microwave-assisted dryers.

However, at least, some of the ideas patented have already been described (by other authors – not necessarily by patent claimers) in the archival or conference literature many years prior to the date of submissions of the initial patent application. A classic case of this type (not in drying area) is the one that made headlines in recent years where a U.S. patent was granted for uses of the remarkable Neem tree which is native to India, but now grown in many parts of the world because of its commercial significance. All parts of this tree – from roots to leaves – have been used in India (and possibly elsewhere) for over two millennia as herbicide, insecticide, pesticide, bactericide as well as for medicinal application. The fact that no one patented this remarkable (but well-known in India and elsewhere in Asia) probably allowed such a patent to be issued and subsequently challenged. It is unlikely that several of the patents awarded can withstand a serious legal challenge due to the fact that they constitute "a prior art" or knowledge already in the public domain, possibly not known to the patent authors.

If one is looking for truly creative ideas for academic research then, in the opinion of the authors, the patent literature is probably not a fertile ground to look for them. As always, there are exceptions to this statement as well.

As far as product-oriented patents are concerned, several patents (up to 28 in some cases in fewer than two years) dealt with the following products (roughly in descending order of numbers issued):

• Hair dryers
• Paper dryers; carpet dryers; dryers for inkjet printed images; photographic film
• Laundry dryers
• Hand dryers
• Dryers for timber, wood; wood wafers
• Dryers for pasta, food products

Among some unusual products for which dryers have been designed and patented are:

• Foot dryers; footwear dryers; nail dryers
• Mascara dryer
• Animal bathing/drying systems
• Hockey equipment dryer
• Animal urine dryers (product used as lure for hunting animals)

Table 3 gives a breakdown of patents issued according to the dryer category. It is interesting that there is great emphasis in the patent literature on low-tech dryers used in the massive consumer market, e.g., dryers for laundry and hair. Contrary to our expectation, the number of innovative dryers for industrial application appears rather infrequently in the patent literature. Perhaps this is a result of the fact that vendors and users of drying systems prefer status quo to the inherent risk involved in adopting new technologies and the cost of patenting inventions with little expectation of commercial exploitation. The long life of most industrial dryers reduces the demand for new dryers.

Table 3. Breakdown of US patents (1998-1999*) according to type of dryer

*January 1998-June 1999 period. Other data are for calendar years.

Design of hair dryers seems to have attracted numerous inventors. The basic drying concept of using heated air blowing over wet hair is intrinsic to all devices patented. Yet, an amazing number of variants have sparked successful patent applications. Among some of the patents awarded in the reporting period, all patents deal with enhancements unrelated to drying itself, e.g., a telescoping handle, dual switch for temperature and air flow control so that the user can grip the dryer handle in different ways, hair curling attachment, air diffusor design, etc. It appears that many of the consumer dryers (hair, hand, clothes, etc.) are motivated more by marketing considerations than by technical considerations.

Many patents cover the design of laundry dryers – a major consumer product, as may be expected. Application of vacuum coupled with infrared heating lamps to supply the heat to wet clothing is the basis of one of the inventions. The risk of fire hazard or scorching has not been mentioned. Another invention deals with use of a cyclone device to collect the lint with lower pressure drop than the current filter systems. It appears to be a good idea but it is not obvious why it was patented in 1998! Use of moisture and temperature sensors to control the clothes dryer is the obvious theme of another invention. Schemes for collection of lint are the subject of several patents related to laundry dryers. Perhaps the most interesting patent in this area is one for "airless drying" which essentially uses superheated steam as the drying medium to enhance the energy efficiency of the laundry dryer; this patents was issued some four years earlier.

Perhaps one of the most interesting inventions for improving energy efficiency in domestic laundry drying – one which one of the authors (ASM) proposed and studied by simulation for a batch grain dryer – relates to the use of a phase change material (PCM) which stores heat as heat of fusion from the exhaust gas of the dryer to improve energy efficiency of the dryer. While the concept is good it is unlikely to be cost-effective. Devahastin et al. (1998) have shown via simulation that it is possible to store part of the sensible heat from the exhaust of the direct dryer in a PCM heat storage system. The energy can then be recovered by pre-heating the dryer inlet air using the stored energy in the PCM. Depending on the PCM and heat exchanger design used, there may be a danger of fire and replacement of the PCM due to loss in performance as a result of repeated cycling.

Several patents have appeared on design of drying systems for ink jet printers, silicon wafers, electronic components, etc. Again, nothing that can be considered truly novel in terms of drying concepts could be identified in the patent abstracts surveyed.

One of the interesting concepts proposed for drying of wet continuous sheets involves use of a stationary cylinder coaxially located with a small clearing within a rotating cylinder, which supports the moving web to be dried. Heat is supplied to the stationery cylinder and is transferred to the rotating cylinder through a layer of low melting point alloy (bismuth, lead, tin, etc.) filling the gap between the two cylinders. While the idea is attractive from a heat transfer point of view, the system is mechanically complex and involves risk of leakage of dangerous fumes. The capital cost is likely to be much higher than simple convection type heating systems or condensing steam cylinders. There is certainly the element of novelty in this invention but it suffers from potential safety, environmental maintenance and high capital cost problems.

Another design for drying of permeable continuous sheets using through drying involves an innovative design of the through dryer roll; the inventor proposes locating a fan at the end of the hollow permeable cylinder which supports the moving web. The idea is to locate the suction device very close to the cylinder itself rather than far away from it.

In summary, an in-depth review of the patent literature pertaining to dryers and drying is necessary before one can make definitive conclusions about the scope and innovative contributions of the patent literature. Our limited survey of the relevant literature uncovered very few truly innovative concepts or processes. Patent activity in the area of large-scale industrial dryers appears to be very limited. The technical literature in the public domain provides a massive minefield for design of novel industrial drying systems when compared to the patent literature. Many patents seem to represent relatively minor variants on patents already issued earlier to the same or other originators. Some patents represented specific applications of previously published work on closely related ideas. A significant number of patents claim originality only of peripheral or superficial interest as far as drying is concerned. Technical literature in the public domain appears to be a more important source for innovative and creative ideas as far as drying technologies are concerned. Examination of the full patent texts is needed before definitive conclusions can be made. Indeed, some of the conclusions of this exploratory work may have to be modified following such a study.

Devahastin, S., Ng, K.W., Mujumdar, A.S., 1998, Preliminary study of a novel thermal storage-spouted bed contactor for particulate drying, 48^th Canadian Chemical Engineering Conference, London, Ontario, Canada.