1、 1 1 Harvest systems and analysis for herbaceous biomass Abstract Biomass feedstocks including crop residues and energy crops hold great potential for energy source. They are currently being considered for use in direct combustion systems and for value added byproducts such as biofuels or biocrude.
2、A major roadblock associated with utilization of biomass feedstocks is the high cost of handling and storage due to low energy and bulk density of these feedstocks. In addition, a wide variety of existing harvest systems creates logistics difficulties for bioenergy industries. The utilization of her
3、baceous biomass requires optimized handling systems to collect, store, and transport year round. This then requires selecting the most economical methods from various existing handling systems for loose and baled biomass materials. How these different harvesting systems can be integrated into a cost
4、-effective supply system is a challenge. The number of harvest days or the window of harvest depends on the type of crops, geographic and climate conditions, soil and nutrient management strategies, etc. The window of harvest could greatly impact on harvest, handling and storage costs. Efficient use
5、 of existing harvesting and handling equipment in a limited harvest window is desired. This chapter provides principles of selecting field harvest machine systems to increase system efficiency and productivity. Practical examples are used to demonstrate cost analysis methods of different harvest sys
6、tems. Field observation results are used to quantitatively describe field capacities of typical biomass harvest and handling machine systems. Optimization models based on typical biomass logistics systems are described. This chapter will guide readers through the decision process to address the meth
7、odology required to design, or specify, a biomass logistics system based on the size of the bioenergy plant being supplied. Cost analysis methods and examples are used to demonstrate components of the process that will enable biorefinery industries and landowners to determine the most cost-effective
8、 way to harvest, store, and transport biomass feedstocks. 1. Introduction Biomass is a distributed energy resource. It must be collected from production fields and accumulated at storage locations. Previous studies of herbaceous biomass as a feedstock for a bioenergy industry have found that the cos
9、ts of harvesting feedstocks are a key cost component in the total logistics chain beginning with a crop on the field and ending with a stream of size-reduced material entering the biorefinery. Harvest of herbaceous biomass is seasonal and the window of harvest is limited. Biomass needs to be stored
10、at a central location. 2 2 Normally, several or many of these central storage locations in a certain range of a biorefinery are needed to ensure 24 hours a day and seven days a week supply. These centralized storage locations are commonly called satellite storage locations (SSL). The size and number
11、 of SSLs depend on the size of the biorefinery plant, availability of biomass within a given radius, window of harvest, and costs. It is convenient to envision the entire biomass logistics chain from fields to biorefineries with three sections. The first section is identified as the “farmgate operat
12、ions”, which include crop production, harvest, delivery to a storage location, and possible preprocessing at the storage location. This section will be administrated by farm clientele with the potential for custom harvest contracts. The second section is the “highway hauling operations,” and it envi
13、sions commercial hauling to transport the biomass from the SSL to the biorefinery in a cost effective manner. The third section is the “receiving facility operations,” and it includes management of the feedstock at the biorefinery, control of inventory, and control of the commercial hauler contract
14、holders to insure a uniform delivery of biomass for year-round operation. Agricultural biomass has low bulk density, and it is normally densified in-field with balers, or chopped with a self-propelled forage harvester. Currently, there are four prominent harvesting technologies available for biomass
15、 harvesting 1. They are: (1) round baling, (2) rectangular baling, (3) chopping with a forage harvester, and separate in-field hauling, and (4) a machine that chops and loads itself for in-field hauling (combined operation). Large round and large rectangular balers are two well-known and widely acce
16、ssible harvesting technologies 2, which offer a range of advantages and disadvantages to farmgate operations. Round bales have the ability to shed water. When these bales are stored in ambient storage, they will store satisfactorily without covering and storage cost is significantly reduced. The rou
17、nd baler, because it is a smaller machine with fewer trafficability issues, can be used for more productive workdays during an extended harvest season over the winter months 3. Large rectangular bales have greater bulk density, ease of transport, and increased baler productivity (Mg/h). However, the
18、 increased capital cost for the large rectangular baler and the bales inability to shed water limit its use on farms in Southeastern United States. Bale compression machines are available to compress a large rectangular bale and produce high-density packages 4. The densified package has two or three
19、 times higher density than the field density of large rectangular bales 5. The goal of an effective logistics system is to streamline storage, handling, and preserve the quality of the biomass through the entire logistics chain. This goal will minimize average feedstock cost across year-round operat
20、ion. The farmer shares the goal to preserve the quality 3 3 of the biomass, and also desires to produce the biomass at minimum cost. To assist in the accomplishment of the mutual objectives of both parties, this chapter will discuss major logistics and machine systems issues starting from the farmga
21、te to the receiving facilities at a biorefinery. Constraints in this biomass supply chain will also be discussed. The impact of different harvest scenarios for herbaceous biomass harvest will be shown. Logistics systems have been designed for many agricultural and forest products industries. Thus, i
22、t is wise to use the lessons learned in these commercial examples. Each of these industries faces a given set of constraints (length of harvest season, density of feedstock production within a given radius, bulk density of raw material, various storage options, quality changes during storage, etc.),
23、 and the logistics system was designed accordingly. Typically, none of these systems can be adopted in its entirety for a bioenergy plant at a specific location, but the key principles in their design are directly applicable. Commercial examples will be used in this chapter to interpret these princi
24、ples. 2. Biomass Harvesting and the Field Performance of Harvest Machine Systems 2.1 Harvesting Harvesting of cellulosic biomass, specifically herbaceous biomass, is done with a machine, or more typically a set of machines, that travel over the field and collect the biomass. These machines are desig
25、ned with the traction required for off-road operation, thus they typically are not well suited for highway operation. Therefore, the transition point between “in-field hauling” and “highway hauling” is critical in the logistics system. In-field hauling is defined as the operations required to haul b
26、iomass from the point a load is created in-field to a storage location chosen to provide needed access for highway trucks. This hauling includes hauling in-field plus some limited travel over a public road to the storage location. Harvesting systems can be categorized as coupled systems and uncouple
27、d systems. Ideal coupled systems have a continuous flow of material from the field to the plant. An example is the wood harvest in the Southeast of the United States. Wood is harvested year-round and delivered directly to the processing plant. Uncoupled systems have various storage features in the l
28、ogistics system. Sugarcane harvesting is an example of a coupled system for herbaceous crops. The sugar cane harvester cuts the cane into billets about 38-cm long and conveys this material into a trailer traveling beside the harvester (Figure 1). The harvester has no on-board storage. Thus, a trailer has to be in place for it to continue to harvest. The trailer, when full, travels to a transfer point where it empties into a truck for highway hauling (Figure 2). Each operation is coupled to the operation upstream and downstream. It requires four tractors, trailers, and
